BZFlag is an open-source tank warfare game. You control (with either mouse or keyboard) a tank that can jump, and navigate it through hundreds of user-generated levels that have many potential variations, both in layout and variables that can be toggled for a specific round. Collect weapons and power-ups ("flags") as you work alone or in a team to achieve your objectives. Gameplay modes include free for all, team free for all, capture the flag, rabbit hunt, king of the hill, and hold the flag. Being able to use the radar to quickly understand the situation is key to avoiding enemy fire and locking in on your target.
BZFlag has an active development and user community, and is free to download and play, either locally or on one of the many hosted servers.