Built this for myself because every focus timer I tried was either too bloated or too basic. FocusFlow stays out of your way - start a session, it disappears from your taskbar and becomes a small floating circle above all your windows. Drag it anywhere. Click to return. Right-click to pause.
Also has session tracking, goals, a GitHub-style activity heatmap, idle detection, and a dashboard. But honestly the floating overlay is the thing.
Free. No account. Windows 10/11