Q4Max adds many features and fixes to Quake 4, making it a much more enjoyable and complete game. For this reason, most servers running Quake 4 are running Q4Max.
Q4Max has the ability to output the results of matches as XML files. These XML files can then be parsed and displayed by MAXStats, a companion php script that builds a summary over all games and ranks players against each other.
In this shot you can see the top 10 players on the server, and also the details of one of those players - you can chose to see the detail of any of their games, and see weapon accuracy stats, kill / death ratios, etc.
If you're a developer, feel free to use the XML files as input for your own tool - just because we have built MAXStats doesn't mean there aren't many more things that can be done using this data.
CPMA (the Quake 3 mod) uses the same format XML files for it's latest stat generation, and MAXStats is compatible with both games.