Sunvox is a modular synth/tracker. I have used it before, and it gets some cool chippy sounds with very minimal hardware requirements.

A web of sound

Features:

* Modular interface.
* Highly optimized synth algorithmes.
* Flexible architecture: SunVox can working on variuos devices. For example: PDA with slow CPU – 16bit sound (fixed point arithmetic); or big PC with powerfull CPU: 32bit sound (floating point arithmetic).
* SunVox engine (without GUI) is open source and distributed under the terms of BSD license.
* Built-in synthesizers:
o FM synthesizer;
o Generator (saw,triangle,square,noise waveforms);
o Sampler (supported formats: WAV, XI);
o SpectraVoice (FFT-based synth for analog-like pads);
o Kicker;
o Stereo Delay;
o Distortion;
o Echo;
o Filter (Low-pass, High-pass, Band-pass, Notch);
o Flanger;
o LFO;
o Loop;
o Reverb (with DC Blocking Filter).
o Vocal Filter
* Supported platforms: Windows, Linux, PalmOS, WindowsCE.
* Export to WAV.