Real hourglasses keep time because sand flows through the neck at a constant rate. Hourglass recreates that physical truth in software: every grain of its simulated sand is metered by the clock, so the top bulb runs empty at the exact moment your timer ends — for any duration from five seconds to twenty-four hours.
Set a time, flip the glass, and watch a deterministic falling-sand simulation pile up grain by grain. When time runs out you get an alarm-grade alert — even if the app is in the background or your phone rebooted along the way.
And because real sand answers real gravity: tilt your phone and the piles lean and avalanche with it. Gravity mode is on by default — your timer stays exactly on time at any angle.