Ruby on Rails
Java, Distributed Systems
If you work on multiple Apache-based Web projects in parallel you probably know this problem: You have to set up a virtual host configuration for every single project on your development machine. It would be very nice to reduce the steps required for this to a minimum. My favorite solution:
Have a directory in your home directory containing symbolic links to your projects - where the names of the links are your local host names.
The following instructions assume you're on Debian/Ubuntu - but "translating" them to other distros or even Windows shouldn't be that hard.