C programs by me:

Typing practice program

Unix style typing program: just a binary, no clutter. You can practice your typing skills while reading your favorite text at the same time. Features: speed/error counts, three types of punishemts when making errors, all in three degrees of severity. Some more features like beeping on/off, highlight errors on/off, go back on errors on/off, hide your typing on/off. The newest version (0.4.3) is not compilable and needs serious work to implement a.o. showing a keyboard layout and highlight the next-to-type character (etc.). Currently development is halted.
Jun 20 2000 Gnu Compr. Tar typing_0.3.5.tar.gz 16464 bytes

Command line arithmethic/logic

You can run this program from the commandline and do simple math and conversions between number systems. This program is probably not the best out there. The only external call the program has is to the write() system call (no math, no nothing).
Jun 28 2000 Gnu Compr. Tar display_bin_0.9.tar.gz 5849 bytes

Analogue Console Clock

Run and see, title says it all (uses ncurses). (manpage (nroff source))
Oct 30 2001 C  program text clockalrm.c 11729 bytes

A Spartan Editor

This editor lets you edit individual bits and/or bit/byte-ranges. Shows bytes as bitstrings, hex values, and (if applicable) ascii characters. It does not grab the screen with ncurses or the like (more like ed). (Very basic editor, probably only usefull if you want to modify some individual bit somewhere in a file, and you know its location).
Okt  7 2000 C program text spartacus.c 8586 bytes

You run these things at your own risk, but they are not virusses/* and don't zap your files on purpose.