Rack747 is a groovebox style synth combining emulated analog synthesis with a flexible wavetable drum module, and a cheesy 16 note sequencer.
It is eminently tweakable, and thoroughly gig-tested: it's my personal notepad, and it could be yours. It also features asynchronous mouse input, keyboard input, and display updating. This BeWare version is a free and uncobbled demo of a commercial version with far expanded functionality. The full tab (commercial) release allows user definable kits, audio file output, and a range of wierd and wonderful addons that offer features such as distorted guitar modelling, and a full instrumental sampler.