Quick thing I made recently on Time Keep (https://www.timekeep.cc) that I'm excited to use: any timer, alarm, countdown, stopwatch, or sleep schedule can be popped out into its own little window and on Chrome/Edge it can be locked over others on your desktop.

On Chrome and Edge it uses the Document Picture-in-Picture API so the window stays on top of everything else while you work. Pause from either window and the state stays in sync (BroadcastChannel turned out to be a good fit for this). Firefox and Safari just use a normal pop-up since neither has shipped Document PiP. On mobile it opens fullscreen in the current tab because phones don't really expose multi-window to the web.

It also requests a wake lock so your screen doesn't fall asleep while a timer's counting down. That matters on a phone where the display would otherwise dim and lock.

The use case that drove me to do this: I'm working, have to do something at X time coming up, and I want a countdown in my face, but it's off on my phone or behind other windows. Now it just sits in the corner where I want it.

(There's also been a bunch of tweaks / new tools added since the last time I posted: a day planner, overlap zones, an "it's 5 o'clock somewhere" page ... for anyone who remembers the v1 HN Show post a month or so ago.)