King of the Server (KotS), in this case the 2007 variant, is a mod that takes regular deathmatch and mixes it up with some RPG elements.
"As you join one of the servers you're prompted to begin a character based on your in-game name. As you start fragging away in a FFA DM setting your character will gain exp points, as well as credits and increase in levels. For each level you grow you gain points that allow you to upgrade weapons and playertrees such as: Strength, Dexterity, Wisdom and Rage."

The character database gets reset tonight so everyone starts at level 0 again and the servers will be crowded!

Links: Q2 Download Quake II KotS, KotS forum, KotS Guide, mIRC #q2kots