iOS: Here's a novel addition to the crowded iOS timer apps space: Humming Timer allows you to set a timer, and then it picks a song from your music library that matches that duration.
If you've seen the classic '90s film Hudson Hawk, you'll recognise Humming Timing's strategy. Just set a timer, and it picks a song (or playlist of songs) that matches that amount of time. When the music stops, your timer is done. You can't go through and change songs, pick moods, or exclude genres, but it's still a fun way to countdown while you're cooking.
Humming Timing (Free) [iTunes App Store]