diff --git a/app/assets/javascripts/discourse/app/components/about-page.gjs b/app/assets/javascripts/discourse/app/components/about-page.gjs
index 9406dd14188..5d929aaa44c 100644
--- a/app/assets/javascripts/discourse/app/components/about-page.gjs
+++ b/app/assets/javascripts/discourse/app/components/about-page.gjs
@@ -9,6 +9,16 @@ import i18n from "discourse-common/helpers/i18n";
 import escape from "discourse-common/lib/escape";
 import I18n from "discourse-i18n";
 
+const pluginActivitiesFuncs = [];
+
+export function addAboutPageActivity(name, func) {
+  pluginActivitiesFuncs.push({ name, func });
+}
+
+export function clearAboutPageActivities() {
+  pluginActivitiesFuncs.clear();
+}
+
 export default class AboutPage extends Component {
   get moderatorsCount() {
     return this.args.model.moderators.length;
@@ -57,7 +67,7 @@ export default class AboutPage extends Component {
   }
 
   get siteActivities() {
-    return [
+    const list = [
       {
         icon: "scroll",
         class: "topics",
@@ -104,6 +114,8 @@ export default class AboutPage extends Component {
         period: I18n.t("about.activities.periods.all_time"),
       },
     ];
+
+    return list.concat(this.siteActivitiesFromPlugins());
   }
 
   get contactInfo() {
@@ -139,6 +151,33 @@ export default class AboutPage extends Component {
     }
   }
 
+  siteActivitiesFromPlugins() {
+    const stats = this.args.model.stats;
+    const statKeys = Object.keys(stats);
+
+    const configs = [];
+    for (const { name, func } of pluginActivitiesFuncs) {
+      let present = false;
+      const periods = {};
+      for (const stat of statKeys) {
+        const prefix = `${name}_`;
+        if (stat.startsWith(prefix)) {
+          present = true;
+          const period = stat.replace(prefix, "");
+          periods[period] = stats[stat];
+        }
+      }
+      if (!present) {
+        continue;
+      }
+      const config = func(periods);
+      if (config) {
+        configs.push(config);
+      }
+    }
+    return configs;
+  }
+
   <template>
     <section class="about__header">
       {{#if @model.banner_image}}
diff --git a/app/assets/javascripts/discourse/app/lib/plugin-api.gjs b/app/assets/javascripts/discourse/app/lib/plugin-api.gjs
index a1ce362174d..bc5a4ff6647 100644
--- a/app/assets/javascripts/discourse/app/lib/plugin-api.gjs
+++ b/app/assets/javascripts/discourse/app/lib/plugin-api.gjs
@@ -3,10 +3,11 @@
 // docs/CHANGELOG-JAVASCRIPT-PLUGIN-API.md whenever you change the version
 // using the format described at https://keepachangelog.com/en/1.0.0/.
 
-export const PLUGIN_API_VERSION = "1.36.0";
+export const PLUGIN_API_VERSION = "1.37.0";
 
 import $ from "jquery";
 import { h } from "virtual-dom";
+import { addAboutPageActivity } from "discourse/components/about-page";
 import { addBulkDropdownButton } from "discourse/components/bulk-select-topics-dropdown";
 import {
   addApiImageWrapperButtonClickEvent,
@@ -3238,6 +3239,45 @@ class PluginApi {
     registerAdminPluginConfigNav(pluginId, mode, links);
   }
 
+  /**
+   * Adds a custom site activity item in the new /about page. Requires using
+   * the `register_stat` server-side API to serialize the needed data to the
+   * frontend.
+   *
+   * ```
+   * api.addAboutPageActivity("released_songs", (periods) => {
+   *   return {
+   *     icon: "guitar",
+   *     class: "released-songs",
+   *     activityText: `${periods["last_year"]} released songs`,
+   *     period: "in the last year",
+   *   };
+   * });
+   * ```
+   *
+   * The above example would require the `register_stat` server-side API to be
+   * used like this:
+   *
+   * ```ruby
+   * register_stat("released_songs", expose_via_api: true) do
+   *   {
+   *     last_year: Songs.where("released_at > ?", 1.year.ago).count,
+   *     last_month: Songs.where("released_at > ?", 1.month.ago).count,
+   *   }
+   * end
+   * ```
+   *
+   * @callback activityItemConfig
+   * @param {Object} periods - an object containing the periods that the block given to the `register_stat` server-side API returns.
+   * @returns {Object} - configuration object for the site activity item. The object must contain the following properties: `icon`, `class`, `activityText` and `period`.
+   *
+   * @param {string} name - a string that matches the string given to the `register_stat` server-side API.
+   * @param {activityItemConfig} func - a callback that returns an object containing properties for the custom site activity item.
+   */
+  addAboutPageActivity(name, func) {
+    addAboutPageActivity(name, func);
+  }
+
   #deprecatedHeaderWidgetOverride(widgetName, override) {
     if (DEPRECATED_HEADER_WIDGETS.includes(widgetName)) {
       this.container.lookup("service:header").anyWidgetHeaderOverrides = true;
diff --git a/app/assets/javascripts/discourse/tests/helpers/qunit-helpers.js b/app/assets/javascripts/discourse/tests/helpers/qunit-helpers.js
index 96f33faeea3..ee1ebae4c16 100644
--- a/app/assets/javascripts/discourse/tests/helpers/qunit-helpers.js
+++ b/app/assets/javascripts/discourse/tests/helpers/qunit-helpers.js
@@ -12,6 +12,7 @@ import MessageBus from "message-bus-client";
 import { resetCache as resetOneboxCache } from "pretty-text/oneboxer";
 import QUnit, { module, skip, test } from "qunit";
 import sinon from "sinon";
+import { clearAboutPageActivities } from "discourse/components/about-page";
 import {
   cleanUpComposerUploadHandler,
   cleanUpComposerUploadMarkdownResolver,
@@ -251,6 +252,7 @@ export function testCleanup(container, app) {
   resetAdminPluginConfigNav();
   resetTransformers();
   rollbackAllPrepends();
+  clearAboutPageActivities();
 }
 
 function cleanupCssGeneratorTags() {
diff --git a/app/assets/javascripts/discourse/tests/integration/components/about-page-test.gjs b/app/assets/javascripts/discourse/tests/integration/components/about-page-test.gjs
new file mode 100644
index 00000000000..df7854af670
--- /dev/null
+++ b/app/assets/javascripts/discourse/tests/integration/components/about-page-test.gjs
@@ -0,0 +1,64 @@
+import { render } from "@ember/test-helpers";
+import { module, test } from "qunit";
+import AboutPage from "discourse/components/about-page";
+import { withPluginApi } from "discourse/lib/plugin-api";
+import { setupRenderingTest } from "discourse/tests/helpers/component-test";
+
+function createModelObject({
+  title = "My Forums",
+  admins = [],
+  moderators = [],
+  stats = {},
+}) {
+  return {
+    title,
+    admins,
+    moderators,
+    stats,
+  };
+}
+
+module("Integration | Component | about-page", function (hooks) {
+  setupRenderingTest(hooks);
+
+  test("custom site activities registered via the plugin API", async function (assert) {
+    withPluginApi("1.37.0", (api) => {
+      api.addAboutPageActivity("my_custom_activity", (periods) => {
+        return {
+          icon: "eye",
+          class: "custom-activity",
+          activityText: `${periods["3_weeks"]} my custom activity`,
+          period: "in the last 3 weeks",
+        };
+      });
+
+      api.addAboutPageActivity("another_custom_activity", () => null);
+    });
+
+    const model = createModelObject({
+      stats: {
+        my_custom_activity_3_weeks: 342,
+        my_custom_activity_1_year: 123,
+        another_custom_activity_1_day: 994,
+      },
+    });
+
+    await render(<template><AboutPage @model={{model}} /></template>);
+    assert
+      .dom(".about__activities-item.custom-activity")
+      .exists("my_custom_activity is rendered");
+    assert
+      .dom(".about__activities-item.custom-activity .d-icon-eye")
+      .exists("icon for my_custom_activity is rendered");
+    assert
+      .dom(
+        ".about__activities-item.custom-activity .about__activities-item-count"
+      )
+      .hasText("342 my custom activity");
+    assert
+      .dom(
+        ".about__activities-item.custom-activity .about__activities-item-period"
+      )
+      .hasText("in the last 3 weeks");
+  });
+});
diff --git a/docs/CHANGELOG-JAVASCRIPT-PLUGIN-API.md b/docs/CHANGELOG-JAVASCRIPT-PLUGIN-API.md
index 771545762ff..c32c02b73d8 100644
--- a/docs/CHANGELOG-JAVASCRIPT-PLUGIN-API.md
+++ b/docs/CHANGELOG-JAVASCRIPT-PLUGIN-API.md
@@ -7,6 +7,10 @@ in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [1.37.0] - 2024-08-19
+
+- Added `addAboutPageActivity` which allows plugins/TCs to register a custom site activity item in the new /about page. Requires the server-side `register_stat` plugin API.
+
 ## [1.36.0] - 2024-08-06
 
 - Added `addLogSearchLinkClickedCallbacks` which allows plugins/TCs to register a callback when a search link is clicked and before a search log is created 
diff --git a/lib/plugin/instance.rb b/lib/plugin/instance.rb
index 725fe7caee1..b41ac15f6c7 100644
--- a/lib/plugin/instance.rb
+++ b/lib/plugin/instance.rb
@@ -1121,6 +1121,9 @@ class Plugin::Instance
   # group of stats is shown on the site About page in the Site Statistics
   # table. Some stats may be needed purely for reporting purposes and thus
   # do not need to be shown in the UI to admins/users.
+  #
+  # TODO(osama): deprecate show_in_ui when experimental_redesigned_about_page_groups
+  # is removed
   def register_stat(name, show_in_ui: false, expose_via_api: false, &block)
     # We do not want to register and display the same group multiple times.
     return if DiscoursePluginRegistry.stats.any? { |stat| stat.name == name }
diff --git a/plugins/chat/assets/javascripts/discourse/initializers/chat-setup.js b/plugins/chat/assets/javascripts/discourse/initializers/chat-setup.js
index 7ed4a6f3728..0a7b2ebe6e3 100644
--- a/plugins/chat/assets/javascripts/discourse/initializers/chat-setup.js
+++ b/plugins/chat/assets/javascripts/discourse/initializers/chat-setup.js
@@ -1,3 +1,4 @@
+import { number } from "discourse/lib/formatter";
 import { withPluginApi } from "discourse/lib/plugin-api";
 import { getOwnerWithFallback } from "discourse-common/lib/get-owner";
 import { replaceIcon } from "discourse-common/lib/icon-library";
@@ -163,6 +164,21 @@ export default {
           document.body.classList.remove("chat-drawer-active");
         }
       });
+
+      api.addAboutPageActivity("chat_messages", (periods) => {
+        const count = periods["7_days"];
+        if (count) {
+          return {
+            icon: "comment-dots",
+            class: "chat-messages",
+            activityText: I18n.t("about.activities.chat_messages", {
+              count,
+              formatted_number: number(count),
+            }),
+            period: I18n.t("about.activities.periods.last_7_days"),
+          };
+        }
+      });
     });
   },
 
diff --git a/plugins/chat/config/locales/client.en.yml b/plugins/chat/config/locales/client.en.yml
index 7d1f101e653..7c52d0b952c 100644
--- a/plugins/chat/config/locales/client.en.yml
+++ b/plugins/chat/config/locales/client.en.yml
@@ -33,6 +33,10 @@ en:
       chat_messages_count: "Chat messages"
       chat_channels_count: "Chat channels"
       chat_users_count: "Chat users"
+      activities:
+        chat_messages:
+          one: "%{formatted_number} chat message"
+          other: "%{formatted_number} chat messages"
 
     chat:
       text_copied: Text copied to clipboard
diff --git a/plugins/chat/plugin.rb b/plugins/chat/plugin.rb
index 51c3eefdcc5..1adfb0376d3 100644
--- a/plugins/chat/plugin.rb
+++ b/plugins/chat/plugin.rb
@@ -18,6 +18,7 @@ register_asset "stylesheets/mobile/index.scss", :mobile
 
 register_svg_icon "comments"
 register_svg_icon "comment-slash"
+register_svg_icon "comment-dots"
 register_svg_icon "lock"
 register_svg_icon "clipboard"
 register_svg_icon "file-audio"
diff --git a/plugins/chat/spec/system/about_page_site_acitivity_spec.rb b/plugins/chat/spec/system/about_page_site_acitivity_spec.rb
new file mode 100644
index 00000000000..64485803da3
--- /dev/null
+++ b/plugins/chat/spec/system/about_page_site_acitivity_spec.rb
@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+describe "Chat messages site activity in the about page", type: :system do
+  fab!(:current_user) { Fabricate(:user) }
+  fab!(:group) { Fabricate(:group, users: [current_user]) }
+
+  let(:about_page) { PageObjects::Pages::About.new }
+
+  before do
+    chat_system_bootstrap
+    SiteSetting.experimental_redesigned_about_page_groups = group.id.to_s
+    sign_in(current_user)
+
+    Fabricate(:chat_message, created_at: 5.hours.ago)
+    Fabricate(:chat_message, created_at: 2.days.ago)
+    Fabricate(:chat_message, created_at: 6.days.ago)
+    Fabricate(:chat_message, created_at: 9.days.ago)
+  end
+
+  it "displays the number of chat messages in the last 7 days" do
+    about_page.visit
+
+    expect(about_page.site_activities.custom("chat-messages")).to have_custom_count(
+      I18n.t("js.about.activities.chat_messages", count: 3, formatted_number: "3"),
+    )
+    expect(about_page.site_activities.custom("chat-messages")).to have_custom_period(
+      I18n.t("js.about.activities.periods.last_7_days"),
+    )
+  end
+end
diff --git a/spec/system/page_objects/components/about_page_site_activity.rb b/spec/system/page_objects/components/about_page_site_activity.rb
index bf369bdfff6..5e0a9a5d7d0 100644
--- a/spec/system/page_objects/components/about_page_site_activity.rb
+++ b/spec/system/page_objects/components/about_page_site_activity.rb
@@ -43,6 +43,14 @@ module PageObjects
           translation_key: "about.activities.likes",
         )
       end
+
+      # used by plugins
+      def custom(name, translation_key: nil)
+        AboutPageSiteActivityItem.new(
+          container.find(".about__activities-item.#{name}"),
+          translation_key:,
+        )
+      end
     end
   end
 end
diff --git a/spec/system/page_objects/components/about_page_site_activity_item.rb b/spec/system/page_objects/components/about_page_site_activity_item.rb
index 56196273366..b0f9b07c644 100644
--- a/spec/system/page_objects/components/about_page_site_activity_item.rb
+++ b/spec/system/page_objects/components/about_page_site_activity_item.rb
@@ -28,6 +28,16 @@ module PageObjects
         period_element.has_text?(I18n.t("js.about.activities.periods.all_time"))
       end
 
+      # used by plugins
+      def has_custom_count?(text)
+        container.find(".about__activities-item-count").has_text?(text)
+      end
+
+      # used by plugins
+      def has_custom_period?(text)
+        period_element.has_text?(text)
+      end
+
       private
 
       def period_element