Hansen Audio

One of the first plugins I've tried in Linux. Well, nice UI (for night sessions;-)), interesting filters (comb sometimes really surprises me) and simple controls. I'd say it resembles me GR-8 by Phuturetone, but with less functionality. No effects (besides delay and distortion), so it should be combined with external ones.

Not the best overall, but definitely worth trying.

K-Whooms is a simple subtractive synth with an easy UI. It will do exactly what you expect it to, and it will not fail to do those things at any point.