PCRobots is (as of this writing) a rather old version of robot combat in an arena - with a twist. Similar programs (CPPRobots, CRobots, etc.) have been around for a very long time now. Here's the twist:
PCRobots uses 'robots' which are actually MS-DOS .COM or .EXE programs that you write yourself (although there are a few samples provided to get you started). Each program is allocated 64k for data, program & stack requirements. This is the main limiting factor for the number of robots being run at once (the "master control program" is a DOS-based application and is therefore limited by DOS's memory allocation provisions). All you need is a compiler and the appropriate library files to link in to your code.
PCRobots allows a large user-defined arena with obstacles in it and allows inter-robot communication (i.e., teamwork). PCRobots uses a cooperative multitasker to share the processor between the robots. This means that robots can do lots of calculations and planning without being penalised.
Robots are configurable, this means that if your strategy suits a fast agile robot, but one which doesn't need a long cannon range, then you can configure the robot to make use of this. Alternatively, you may want a slow robot with lots of armour.