diff --git a/activity_feed.go b/activity_feed.go
new file mode 100644
index 0000000..c0406b1
--- /dev/null
+++ b/activity_feed.go
@@ -0,0 +1,137 @@
+package mujica
+
+import (
+	"cmp"
+	"log/slog"
+	"time"
+
+	"github.com/egoist/mygo/ui"
+
+	"mujicaui/icons"
+	"mujicaui/theme"
+)
+
+// Activity is one event of an ActivityFeed: Actor did Action to Object at Time.
+type Activity struct {
+	ID     string
+	Actor  string
+	Action string
+	Object string
+	Time   time.Time
+}
+
+// ActivityFeedOptions configure an ActivityFeed.
+type ActivityFeedOptions struct {
+	// Location decides which day an event falls on; nil is time.Local.
+	Location *time.Location
+	// Today fixes the day called Today; zero uses the clock.
+	Today Date
+}
+
+// activityRow is a day header (item -1) or an event.
+type activityRow struct {
+	day  Date
+	item int
+}
+
+// activityFeedCache keeps the grouped rows until the count, first or last event, or location changes.
+type activityFeedCache struct {
+	n           int
+	first, last string
+	loc         *time.Location
+	rows        []activityRow
+	scroll      ui.ScrollState
+	sized       bool
+}
+
+// ActivityFeed lists events grouped by day, newest first as given, building only the rows in view.
+func ActivityFeed(c *ui.Context, items []Activity, opts ActivityFeedOptions) *ui.Element {
+	loc := cmp.Or(opts.Location, time.Local)
+	for _, a := range items {
+		if a.ID == "" || a.Actor == "" || a.Action == "" || a.Time.IsZero() {
+			panic("mujica: ActivityFeed event needs an ID, Actor, Action and Time")
+		}
+	}
+	k := Tokens(c)
+	d := Density(c)
+	sc := ui.Scroll(c).MinHeight(0).Role(ui.RoleList).Label(msg(c, "activity_feed.label"))
+	if len(items) == 0 {
+		sc.Children(func() {
+			EmptyState(c, EmptyStateOptions{Title: msg(c, "activity_feed.empty"), Description: msg(c, "activity_feed.empty_hint"), Icon: icons.Must("clock")})
+		})
+		return sc
+	}
+	cache := *ui.Local(sc, "activity_feed", func() *activityFeedCache { return &activityFeedCache{} })
+	sc.TrackScroll(&cache.scroll)
+	if cache.n != len(items) || cache.first != items[0].ID || cache.last != items[len(items)-1].ID || cache.loc != loc {
+		cache.n, cache.first, cache.last, cache.loc = len(items), items[0].ID, items[len(items)-1].ID, loc
+		cache.rows = cache.rows[:0]
+		var prev Date
+		for i, a := range items {
+			if day := DateOf(a.Time.In(loc)); day != prev || i == 0 {
+				cache.rows = append(cache.rows, activityRow{day: day, item: -1})
+				prev = day
+			}
+			cache.rows = append(cache.rows, activityRow{item: i})
+		}
+		slog.Debug("mujica: activity_feed grouped", "events", len(items), "rows", len(cache.rows))
+	}
+	rowH := d.ControlHeight() + 2*d.Unit()
+	view := sc.Bounds()
+	if view.H == 0 && !cache.sized {
+		// Unmeasured: build again once the box has its height.
+		cache.sized = true
+		c.Invalidate()
+	}
+	first := max(0, int(cache.scroll.Y/rowH)-2)
+	last := min(len(cache.rows), int((cache.scroll.Y+max(view.H, rowH))/rowH)+3)
+	today := datetimeToday(c, opts.Today)
+	sc.Children(func() {
+		ui.Box(c).FillWidth().Height(rowH * float32(len(cache.rows))).Children(func() {
+			for r := first; r < last; r++ {
+				row := cache.rows[r]
+				box := ui.Row(c).Key(r).Absolute().Left(0).Right(0).Top(rowH*float32(r)).Height(rowH).
+					AlignItems(ui.Center).Gap(d.Unit()*3).Padding(0, d.Unit()*3)
+				if row.item < 0 {
+					activityFeedHeader(c, k, box, row.day, today)
+					continue
+				}
+				activityFeedEvent(c, k, box, items[row.item], loc)
+			}
+		})
+	})
+	return sc
+}
+
+// activityFeedHeader is a day's title: Today, Yesterday or the date, over an ornament rule.
+func activityFeedHeader(c *ui.Context, k theme.Tokens, box *ui.Element, day, today Date) {
+	label := datetimeDayLabel(c, day)
+	switch day {
+	case today:
+		label = msg(c, "activity_feed.today")
+	case today.AddDays(-1):
+		label = msg(c, "activity_feed.yesterday")
+	}
+	box.Role(ui.RoleText).AlignItems(ui.End).Padding(0, Density(c).Unit()*3, Density(c).Unit(), Density(c).Unit()*3)
+	box.Draw(func(p *ui.Painter, r ui.Rect) { p.Fill(ui.Rect{X: r.X, Y: r.Y + r.H - 1, W: r.W, H: 1}, k.Ornament, 0) })
+	box.Children(func() {
+		ui.Text(c, label).Font(theme.SerifFont).FontSize(FontSize(c, theme.CaptionSize+1)).FontWeight(600).TextColor(k.Text).SingleLine()
+	})
+}
+
+// activityFeedEvent is one event: avatar, "Actor action Object", and the time.
+func activityFeedEvent(c *ui.Context, k theme.Tokens, box *ui.Element, a Activity, loc *time.Location) {
+	when := a.Time.In(loc).Format("15:04")
+	box.Role(ui.RoleListItem).Label(a.Actor + " " + a.Action + " " + a.Object + ", " + when)
+	box.Children(func() {
+		Avatar(c, a.Actor, AvatarOptions{Size: 28})
+		ui.Row(c).Grow(1).Shrink(1).MinWidth(0).Gap(4).Children(func() {
+			ui.Text(c, a.Actor).Bold().TextColor(k.Text).SingleLine().Shrink(0)
+			ui.Text(c, a.Action).TextColor(k.TextMuted).SingleLine().Shrink(0)
+			if a.Object != "" {
+				ui.Text(c, a.Object).TextColor(k.AccentText).SingleLine().Shrink(1).Ellipsis("…")
+			}
+		})
+		ui.Text(c, when).TextColor(k.TextMuted).FontSize(FontSize(c, theme.CaptionSize)).FontFeatures("tnum").SingleLine()
+	})
+}
diff --git a/activity_feed_test.go b/activity_feed_test.go
new file mode 100644
index 0000000..2d408de
--- /dev/null
+++ b/activity_feed_test.go
@@ -0,0 +1,92 @@
+package mujica
+
+import (
+	"strconv"
+	"testing"
+	"time"
+
+	"github.com/egoist/mygo/ui"
+)
+
+func feedItems(n int) []Activity {
+	base := time.Date(2026, 10, 5, 18, 0, 0, 0, time.UTC)
+	out := make([]Activity, n)
+	for i := range out {
+		out[i] = Activity{ID: strconv.Itoa(i), Actor: "Mira", Action: "edited", Object: "Doc " + strconv.Itoa(i), Time: base.Add(-time.Duration(i) * 5 * time.Hour)}
+	}
+	return out
+}
+
+func TestActivityFeedGroupsByDay(t *testing.T) {
+	items := feedItems(6) // 18:00, 13:00, 08:00, 03:00 on the 5th, then 22:00 and 17:00 on the 4th
+	tt := ui.NewTester(func(c *ui.Context) {
+		Use(c, Settings{})
+		ActivityFeed(c, items, ActivityFeedOptions{Location: time.UTC, Today: Date{2026, 10, 5}}).Size(600, 500)
+	}, 640, 540)
+	tt.Frame()
+	for _, s := range []string{"Today", "Yesterday", "Mira edited Doc 0, 18:00", "Mira edited Doc 4, 22:00"} {
+		if _, ok := tt.Find(s); !ok {
+			t.Errorf("missing %q in %q", s, tt.Texts())
+		}
+	}
+	today, _ := tt.Find("Today")
+	yest, _ := tt.Find("Yesterday")
+	doc3, _ := tt.Find("Mira edited Doc 3, 03:00")
+	doc4, _ := tt.Find("Mira edited Doc 4, 22:00")
+	if !(today.Y < doc3.Y && doc3.Y < yest.Y && yest.Y < doc4.Y) {
+		t.Fatalf("order: today %v, doc3 %v, yesterday %v, doc4 %v", today, doc3, yest, doc4)
+	}
+	// Another zone moves 03:00 UTC to the previous day.
+	tt2 := ui.NewTester(func(c *ui.Context) {
+		Use(c, Settings{Locale: ZhCN})
+		ActivityFeed(c, items, ActivityFeedOptions{Location: time.FixedZone("W", -5*3600), Today: Date{2026, 10, 5}}).Size(600, 500)
+	}, 640, 540)
+	tt2.Frame()
+	if _, ok := tt2.Find("Mira edited Doc 3, 22:00"); !ok || !tt2.HasText("今天") || !tt2.HasText("昨天") {
+		t.Fatalf("zone texts %q", tt2.Texts())
+	}
+}
+
+func TestActivityFeedVirtualizesAndEmpty(t *testing.T) {
+	items := feedItems(100000)
+	tt := ui.NewTester(func(c *ui.Context) {
+		Use(c, Settings{})
+		ActivityFeed(c, items, ActivityFeedOptions{Location: time.UTC, Today: Date{2026, 10, 5}}).Size(600, 400)
+	}, 640, 440)
+	tt.Frame()
+	if n := len(tt.Texts()); n == 0 || n > 120 {
+		t.Fatalf("built %d texts for 100000 events", n)
+	}
+	tt.Scroll(100, 100, 0, 2000000)
+	tt.Frame()
+	if _, ok := tt.Find("Mira edited Doc 0, 18:00"); ok {
+		t.Fatal("first event still built after scrolling far")
+	}
+	tt3 := ui.NewTester(func(c *ui.Context) {
+		Use(c, Settings{})
+		ActivityFeed(c, nil, ActivityFeedOptions{}).Size(400, 300)
+	}, 440, 340)
+	if !tt3.HasText("No activity yet") {
+		t.Fatalf("empty: %q", tt3.Texts())
+	}
+	defer func() {
+		if recover() == nil {
+			t.Fatal("event without ID accepted")
+		}
+	}()
+	ui.NewTester(func(c *ui.Context) {
+		Use(c, Settings{})
+		ActivityFeed(c, []Activity{{Actor: "x"}}, ActivityFeedOptions{})
+	}, 200, 100)
+}
+
+func TestActivityFeedSnapshot(t *testing.T) {
+	items := feedItems(5)
+	items[1].Actor, items[1].Action, items[1].Object = "Lin", "commented on", "Quarterly report"
+	items[3].Actor, items[3].Action, items[3].Object = "Sakiko", "approved", "Merge request !42"
+	snapshot(t, "activity_feed", 520, 320, func(c *ui.Context) {
+		ui.Column(c).Padding(12).Children(func() {
+			ActivityFeed(c, items, ActivityFeedOptions{Location: time.UTC, Today: Date{2026, 10, 5}}).Size(496, 296)
+		})
+	})
+}
diff --git a/messages_essentials.go b/messages_essentials.go
index 5c9e9d2..4c8abe1 100644
--- a/messages_essentials.go
+++ b/messages_essentials.go
@@ -36,6 +36,12 @@ func init() {
 		"dock_panel.zone3": {"Bottom dock", "底部停靠区"},
 		"dock_panel.hint":  {"Drag to an edge, or Shift+Alt+arrow, to dock", "拖到边缘，或按 Shift+Alt+方向键停靠"},
 
+		"activity_feed.label":      {"Activity", "活动"},
+		"activity_feed.today":      {"Today", "今天"},
+		"activity_feed.yesterday":  {"Yesterday", "昨天"},
+		"activity_feed.empty":      {"No activity yet", "暂无活动"},
+		"activity_feed.empty_hint": {"Changes people make will show here.", "成员的操作会显示在这里。"},
+
 		"qr_code.label":    {"QR code", "二维码"},
 		"qr_code.too_long": {"Text too long for a QR code", "文字过长，无法生成二维码"},
 	})
diff --git a/resizable_panel_group_test.go b/resizable_panel_group_test.go
index 7deb347..6c56463 100644
--- a/resizable_panel_group_test.go
+++ b/resizable_panel_group_test.go
@@ -106,7 +106,10 @@ func TestResizablePanelGroupRejects(t *testing.T) {
 				}
 			}()
 			s := tc.sizes
-			ui.NewTester(func(c *ui.Context) { Use(c, Settings{}); ResizablePanelGroup(c, &s, tc.panels, ResizablePanelGroupOptions{}) }, 300, 200)
+			ui.NewTester(func(c *ui.Context) {
+				Use(c, Settings{})
+				ResizablePanelGroup(c, &s, tc.panels, ResizablePanelGroupOptions{})
+			}, 300, 200)
 		}()
 	}
 }
diff --git a/testdata/snapshots/darwin/activity_feed-dark.png b/testdata/snapshots/darwin/activity_feed-dark.png
new file mode 100644
index 0000000..b6a09e5
Binary files /dev/null and b/testdata/snapshots/darwin/activity_feed-dark.png differ
diff --git a/testdata/snapshots/darwin/activity_feed-light.png b/testdata/snapshots/darwin/activity_feed-light.png
new file mode 100644
index 0000000..9e25971
Binary files /dev/null and b/testdata/snapshots/darwin/activity_feed-light.png differ