I stumbled across PHP-TextDB while helping a friend find a viable database she could use on her non-mySQL account. PHP Text DB API is a bare-bones flat-file database that stores its tables in plain text files. Although I wouldn’t use it for huge amounts of data, it’s actually quite nimble and full featured. And it’s under active development, unlike some other options I looked at. Its SQL support is limited, but probably covers 95% of all applications.

As an open source project, it allows you to muck with the code if neccessary. This is actually the second project where I had the need and ability to contribute—which is rather neat. In this case, I optimized one of their comparison functions to be about 25 times faster.