WebDrum
This post is about 10 years old. The information it contains may be out of date and references to software or other products may be obsolete.
WebDrum is a WebAudio drum synthesizer that uses my WebNoise and WebAHDSR projects. Each WebDrum instance can be configured to produce a single drum sound. You can create as many instances as browser performance will allow to produce a varied drum set.
Speaking of browser performance, Chrome currently handles projects with large or complex audio graphs better than Firefox or Safari, so I recommend running WebDrum under Chrome.