Frescobaldi is a LilyPond sheet music editor with built-in MIDI player and PDF preview. It aims to be powerful, yet lightweight and easy to use.
prodatum is a patch editor for the E-MU Proteus 2000 sample-based synthesizer family.
An audio time-scaling library.
A lightweight library containing a number of classes and functions to ease the task of programming GTK+ programs with C++ in POSIX environments.