An interesting synth that can be used as a basic beat box, with the additional capability to make some non-drum synth sounds.
The clap, closed hihat, open hihat, ride and crash are sampled and you have some basic control over how they sound (the included samples are good, and the docs also tell you how to use your own samples if you want). There are also 4 simple but synths that can make some pretty respectable kicks & snares, as well as other non-drum sounds. These synths each have a sine oscillator, a noise generator, two LFOs (one is tempo-synced) and a random S&H oscillator, a couple of envelope controls, and some other basic stuff.
While there are other free drum synths that will probably serve as better choices as a go-to vsti, completists or those looking for new sounds might be interested in onkot for the synths, which offer a couple of features not usually found in simple drum synths (the S&H, pan LFOs, pitch attack).