Scconfig is a single-layer, modular autotools replacement written in ANSI-C (C89). It's been tested on a dozen different UNIX-like operating systems (including Linux, Windows and Mac OS X).
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 code coverage tester.
A distributed PHP search engine and crawler.