Satrap is a simple utility for assembler programers who are creating some bootable programs. It takes the program, adds a boot-loader and creates a bootable floppy.
Useful for creating OS independent programs like memory testers, BIOS and firmware rewriters or CMOS editors or just as an 8086 assembler exercise.
Phalanx is a chess playing engine with agresive playing style. It does not have its own graphical interface, but can be used with general chess interface Xboard (Winboard) by Timm Mann. There is also a commercial version that runs as a native Fritz module and thus can be used with the Fritz graphical interface.
SymPy is a Python library for symbolic mathematics. It aims to become a full-featured computer algebra system (CAS) while keeping the code as simple as possible in order to be comprehensible and easily extensible. SymPy is written entirely in Python and does not require any external libraries.
Real pdf editor. You can use either many already present script functions, or you can create your own, or you can use low level object tree with knowledge of pdf specification to do almost everything with your pdf.