Recently I took over the development of Alsa Modular Synthesier (AMS), an open source software synthesizer for Linux. The last version is from 2004 and it was abandoned since. It got a clumsy interface and cpu hunger but also features the best analogue sound simulation on Linux imho, and sometimes this is the thing you need.
I try to optimize it a bit but its difficult. Good sound comes with a cost it seems and I will try to implement additional filters and oscillator which didnt tax the cpu that much.
Check it out at