ff3sudoku is an add-on that features an engine for playing Sudoku puzzles. It can generate random puzzles, but it also detects and imports Sudokus from several Web sites, including websudoku.com, sudokupuzz.com, sudoku.com.au, and others. There is also a stand-alone version working in Firefox 3+ and GoogleChrome.
liboping is a C library for measuring network latency using ICMP echo requests. It can send to and receive packets from multiple hosts in parallel, which is nice for monitoring applications. Both IPv4 and IPv6 are supported transparently for the programmer and user. A program called oping is included to show the simplicity and potential of the library and provide the functionality at the command line.
InteLib is a library of C++ classes that lets you do Lisp/Scheme programming within your C++ programs, even without any additional preprocessing, without all those calling conventions. You can write code that is accepted by a C++ compiler while thinking in a "Lisp/Scheme mode", and the code you write will look much like Lisp/Scheme code, although it will be pure C++.
HickUP is a small multi-platform system for managing applications for a user or project environment. The user can, through a GUI or command line tool, choose which applications and versions they want to use. The project manager can specify allowed applications and versions of these the project members can select. The user can then select one of multiple environments to use at login or within a specific shell.