What contest logging software exists for the GNU/Linux operating system?
I've used CQRLOG which is built on MySQL but otherwise has many of the same features as other loggers and is fully customizable. If that's too much and you're looking for a simpler solution, Xlog is a barebones logger that can still interchange data with some of the Linux PSK and other digital mode software. Both support all the popular export formats, including adif and Cabrillo. The Arch Linux Wiki has links to another 8 programs that might help, including YFKtest or TLF if you're looking for a barebones console logger or FDLog with field-day-specific features and networking.
A simple way to get a Linux logger is to use a windows logger under WINE Windows Program Loader, or something similar. I've done it before and it works fine, however it can cause problems on a slow computer.
Apart from being much easier and convenient to use than Wine, my success rate with CrossOver is also a bit higher. Furthermore, I have no problem opening my wallet for this decently priced software in support of this company. (Disclosure: No conflict of interests.)