Killzone is sci-fi skirmish wargame, which is based on the current 5th edition rules for Warhammer 40K, as well as the current army lists.
The system was inspired by Games Workshop's Kill Team, a skirmish game based in the Warhammer 40K universe and released in the 4th edition of Warhammer 40K.
Special Operations: Killzone v3 was released in January of 2012, and was developed by a dedicated group of wargamers with a deep passion for the hobby.
The Rules: Special Operations: Killzone Rulebook (download)
The rules have been modified for smaller scale skirmish games. Notable modifications to the 5th Edition rules include - terrain, movement, no vehicles, no deepstriking, turn zero, list restrictions and the overwatch ability.
Your Kill Team: Codex: Operatives (download)
A team consists of 5-20 models. In game, each model within this team operates as a unit of one. No single model can total more than 80 points, and your team cannot total more than 250 points. HQ choices and unique characters are not permitted.
Codex: Operatives specifies which units, and how many unit leaders, can be taken from each Army Book.
Killzone has it's own list of optional Killzone model upgrades, which are divided into Skills and Wargear.
Further restrictions to the team composition are outlined in both the Rulebook and Codex: Operatives. These restrictions can be bypassed by creating themed lists.
So I spent another night digging through my old models and will be posting some Kill Teams lists of my own shortly!