AlsaModularSynth is a realtime modular synthesizer and effect processor. It features MIDI controlled modular software synthesis, realtime effect processing with input capture, full control of all synthesis and effect parameters via MIDI, an integrated LADSPA browser with search capability, and JACK support.
SpectMorph allows you to analyze samples of musical instruments and to combine them (morphing). It can be used to construct hybrid sounds, e.g. a sound between a trumpet and a flute, or smooth transitions, e.g. a sound that starts as a trumpet and then gradually changes to a flute. Interpolating between two samples of the same instrument (different attack velocity of a piano) could be interesting. The analysis process decomposes samples into a sum of sine waves (corresponding to the partials present in the signal, or the part of the signal perceived as "tone") and additional noise. SpectMorph is thus based on the research on Spectral Modelling Synthesis.
hexter is a software synthesizer that models the sound generation of a Yamaha DX7 synthesizer. It can easily load most DX7 patch bank files, edit those patches via a built-in editor or MIDI sys-ex messages, and recreate the sound of the DX7 with greater accuracy than any previous open source emulation (that the author is aware of). It operates as a plugin for the DSSI Soft Synth Interface.