libmidixx is a C++ library to manipulate MIDI sequences. It is intended for a multimedia application that handles playback, recording, and editing of MIDI sequences, though the current version just implements playback only. libmidixx supports OSS, ALSA, and serial (tty) MIDI ports, and also comes with a user-space sequencer implementation, which does a fair job on a lightly-loaded machine.
libSap is linux port of windows' SAP Library which is a software emulation of CPU 6502 microprocessor and Pokey chip. Those two chips are used in Atari XL/XE computers. SAP Library is used to run programs written in 6502 machine language that are using the Pokey chip to play tunes and sounds.
Wine is an implementation of the Windows API on top of X and Unix. It does not require Microsoft Windows, but can use native Windows DLLs if they are available. It provides both a development toolkit for porting Windows source code to Unix as well as a program loader, allowing many unmodified Windows programs to run on x86-based Unixes.
SDL_sif is a simple addon library for SDL for defining areas in which to catch events. Areas can be everything from simple rectangles and polygons to combinations of more advanced shapes, like union, difference, and so on. Once an area is set up, you will receive SDL events with information about what happened where.