The commodore 64 was the best computer in its day for sound creation. Inside, there is a proprietary chip that was basically an analogue synth, with filters and all! this allowed it to produce totally different and, for its day, rich sounds for games. This set of samples comprise some of the more useful percussive sounds straight from the computer. There is now a midi synth built around the C64 chip, called the Sid Station.

Dr Tiricc was a great speech synthesis program for the Atari ST. The plan with this kit was to try to get the program to do human beat box type sounds. These came out well, with about half of the sounds being quite close to drum sounds (albeit in a very crunchy digital manner), while the rest sound quite vocal.

Avalon was a sound editing program made by Steinberg for the Atari ST. As well as the usual cut and paste features it had a synthesiser section. This was modular, and had lots of features I haven't seen since (phase distortion?). The only drawback was it took some time to calculate the sound, but I found it to be a great tool for the production of never-heard-before sounds. There are three kits worth of samples from this fantastic program.

More refined than the last two Avalon kits.

An almost outright games machine, the Atari 800 samples in this library are some of my favorite. Really crunchy and electronic sounding, these samples fit in and cut through most types of electronic dance music in a fine style.

Although not exactly a "computer", these two 'toys' sound like they fit into this category. The Casio VL-tone is something of a classic synth, a tiny but programmable toy. Apparently it was used for an entire backing track by Depeche Mode!
The galaxy invader 2000 is a old style"pocket" computer game, in the space invaders style.

A harder and punchier kit than the Avalon 1