Diep.io

Diep.io is a game similar to that of agar.io and slither.io. You control a small tank, and shoot at small shapes called Polygons and other players to level up, and upgrade your tank in these 8 stats: After every level up, you are able to select to upgrade one of those stats from a menu like the one seen here. You are also able to use the top number keys, 1-8, on a keyboard to select the stat you want to upgrade.
 * Health Regen
 * Max Health
 * Body Damage
 * Bullet Speed
 * Bullet Penetration
 * Bullet Damage
 * Reload
 * The_skill-tree.pngent Speed