Hnefatafl is an implementation of the Norse board game. Hnefatafl 11x11, 13x13, Tablut, and many other variants are supported using rulesets. There is a command-line interface and an X interface (the latter is optional).
Sejd is a very basic line editor which is intended to be a middle ground between "cat" and "ed". It only uses the C89 standard library.
A fast C++ matrix library with an API similar to Matlab's.
A shell library intended for Unix sysadmins.