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.
Smurf is a GTK-based SoundFont editor. SoundFont files are a collection of audio samples and other data that describe instruments for the purpose of composing music. SoundFont files do not describe the music itself, but rather the sounds of the instruments. These instruments can be composed of any digitally recordable or generated sound. This format provides a portable and flexible sound synthesis environment that can be supported in hardware or software. Note that Swami is the successor to Smurf and is an entire object-oriented rewrite of it.