Qsynth is a software synthesizer from the Linux Sound Architecture (LSA) project. It is designed to be a powerful and easy-to-use tool for creating realistic and musical sounds with a MIDI controller. The program offers a range of features, such as a wide range of synthesis engines, filters, envelopes, and effects. Additionally, it allows users to control parameters and apply modulation to create new sounds. It can be used to create sounds for a variety of applications, including music production, sound design, and sound effects.
I use both. Phasex is resource hungry, so I make sound sources from the sounds I generate and play them from qsynth (1 instance) or fluidsynth (2 instances in my stage setup). Phasex is a real synth and very powerful.
VirtualMIDISynth
Tyrell N6
Absynth
AudioMulch
FluidSynth
Skale Tracker
TAL-NoiseMaker
Podolski
Zebralette
The discontinued online version is no longer available. The latest desktop version, v0.81, released in December 2005, is still downloadable and usable.