Beepola is a Windows-based tracker for the ZX Spectrum 48K's beeper speaker. It is capable of assembling songs for use on hardware or emulators, exporting assembly code, rendering songs to WAV, or importing song tables from its supported sound engines from Z80 or TAP files.
Beepola consists of several different "beeper engines" which grant different instrument and effect abilities, all of which have 2 tone channels. As of v1.06, these are:
Has 4 different percussion sounds
Sustain effects can be used
The Music Box
Notes all have a duration of one row
Square wave tones
The Music Studio
Supports 13 different percussion sounds
Supports either Digital Drums samples (8 sounds) or Synth Drums (9 sounds)
Channel 2 has an instrument editor which can produce pitching, detuning and phasing effects.
Up to 100 instruments are supported
5 different percussion sounds
Supports glissando effects
Has an ornament editor which can be used by both channels. Can support up to 31 different ornaments.
Skew and Xor effects can change the timbre of sounds.
FX column that can produce additional (and interesting) sounds
Documentation is also available at the provided link.