Timwi 

Provides functions for implementing programs that can install and uninstall themselves as Windows services.

Contains many classes, structs, and helper functions to deal with 2D geometry (points, lines, curves, etc.)

Solve or generate logic puzzles, including Sudoku (its main focus), Masyu, Nonogram, Slitherlink etc., or fill crossword puzzles and other word grids.

A library to work with 3D models (.obj files).

A library to work with XML files that I personally find more convenient/pleasant to use than XDocument.

Flexible regular expressions on arbitrary object collections