Set a target date and time and this counts down to it in days, hours, minutes, and seconds, or flip it into a simple duration timer if you just need to track elapsed time. Fullscreen mode and a sound alert make it usable as a stage countdown or a shared screen at an event, and presets let you jump back to a countdown you've used before.
The countdown itself is just math against a fixed target time, so closing and reopening the tab (or using the shareable link) recalculates the remaining time correctly — it doesn't rely on the tab staying open to "keep counting" in the background.
The display switches to a "time's up" state and plays the sound alert if you've enabled it, so it's noticeable even if you're not staring at the screen at that exact moment.
Yes — the shareable link encodes your target date and settings, so opening it on another device or sending it to someone else shows the same countdown ticking down to the same moment.