Yes, yes, we know—most people can simply use VLC Player, or burn a video to DVD. If you need to play a video on a system without a DVD drive, though, or make it seriously simple for someone to watch ("Put disc in drive. Restart. Done"), MoviX2 fits the bill.
Terminal-savvy Linux and Windows users can hack together an ISO with their video of choice if they'd like, or use one of the graphical options at the project site—Windows users should grab MoviX2 and the most recent package ending in .exe and follow these instructions, while Linux users can just grab the latest MoviX2 files. Need more help? Check out the MoviX2 documentation, and you'll find it's not too hard to get a disc imaged and burned with a bundled MPlayer—which means it handles a whole heck of a lot of formats and codecs.
MoviX2 is a free download for Windows and Linux systems only.