Here is something eti and I created for BeOS many years ago (1996-2000). I ported it to Mac OS X and still use it, although the synth engine and most of the modules have been completely rewritten over the years.
ObjektSynth 2 features at a glance
General InfoPolyphonic -- up to 127 voices per patch
Modular programming -- up to 127 modules per patch, countless routing and modulation possibilites
Multi-Timbral -- up to 127 patches at a time
MIDI Controllable -- use real knobs of any MIDI fader box, MIDI sequencers, MIDI instrument controllers
Hardware-like latency -- may be the fastest real-time software synth in the world
Expressive Control -- modulate parameters with MIDI CCs, key tracking, velocity, and aftertouch simultaneously
Real-Time -- no samples or wavetables used
ModulesOscillator -- DVCO w/ hard sync, Phase, PWM, linear and exponential FM, advanced glide options
Oscillator waveforms -- Saw up, Saw down, Square (PWM), Triangle, Sine, Noise (pitched)
Filters -- all have key tracking +/- 200% w/ variable center note, FM, self-oscillating resonance
Multimode Filter -- 12 dB per oct., simultaneous Lowpass, Bandpass, Highpass and Notch outputs
Filter X - Ten modes: switchable 12/24dB per oct. x switchable Lowpass, Highpass, Bandpass, Notch and Resonator
Envelope Generators -- all have minimum and maximum level control, sync input, sync outputs for every segment
ADSR -- w/ Hold, continuously adjustable slopes for attack, decay, and release
ASR -- has Looping (use it like an LFO), Hold, continuously adjustable slopes for attack, and release
LFO -- DLFO w/ note sync, Phase, PWM, linear and exponential FM, can be cycled very slowly (hours) with no perceptible stepping
LFO Waveforms -- Saw up, Saw down, Square (PWM), Triangle, Sine, Random Step, Random Ramp
Ring Modulator -- has optional built-in sine oscillator w/ FM
Distortion -- w/ clipping, hard and soft distortion types
Noise -- White, Pink and Brownian
Control Mixer -- Combine, layer, scale, change offset of LFOs, EGs, and Noise modules
Delay -- smoothly changes pitch of repeats as you change delay time, up to 10 second delay time
Delay as oscillator -- has adjustable 6dB lowpass rolloff and up to two-octave key tracking for simple physical modelling
Other modules -- 3 Input Mixer, 6 Input Mixer, Amplifier, Mono Out, Stereo out, Pan, Crossfader
Rename modules -- make up functionally descriptive names like "Filter Envelope" or "Kookaburra Oscillator"
Ins and OutsHi-Fi output -- 24-bit, up to 96kHz output support (32-bit floating point internal)
Multiple MIDI sources -- patches can accept MIDI input from more than one MIDI port or application at a time
BeOS New Media Kit support -- will work in concert with other BeOS media kit applications
Multi-output -- assign patches to one or more outputs
Requirements BeOS 5 or greater, with Media/Audio Settings set to enable real-time audio
MIDI controller (eg: keyboard, sequencer, etc.) strongly recommended
