Pixel Knights provides your a virtual arena, you can have friends come in and fight.

https://lh3.googleusercontent.com/-QwcfWSaKQJw/VqFd9E_jneI/AAAAAAAAJA0/m61rPoXQd8s/s800-Ic42/pixel-knights.k4.gif

The controls are WASD with IJKL for shooting bullets. You can eat ($) for points, chat with others. It is designed with client and server, so you will need to connect a server to play.

It has four map, the one above is default square map, there is also split, hall, and sniperArea. You can supply the map number when starting the server.

Pixel Knights was created by Markus Palonen on 2015-02-08, written in C (gnu99) under the MIT License, currently git-1064d62i (2016-01-21).