Gear Up is described as 'multiplayer game where you build customized tanks and battle online opponents in deathmatch, team deathmatch and conquest'. There are three games similar to Gear Up for a variety of platforms, including Linux, Windows, Steam, Android and Android Tablet. The best alternative is CATS: Crash Arena Turbo Stars, which is free. Other Gear Up like games are ROBOCRAFT (Freemium) and Procelio Game (Free).
Procelio is a multiplayer sandbox game where you build a robot out of modular parts, put guns on it, and go fight other people online. Procelio attempts to create a well polished game which players of all skill levels can enjoy.