Aylet plays music files in the `.ay' format. These files are essentially wrappers around bits of Z80 code which play music on the Sinclair ZX Spectrum 128's sound hardware - either the beeper, or (eponymously) the AY-3-8912 sound chip. Files using the Amstrad CPC ports are also supported.

One source of `.ay' files playable with aylet-gtk is "Project AY" on the World of Spectrum website: