Diep.io

Diep.io is a 2-D MMO game similar to that of Agar.io, Slither.io and Wings.io. You control a simple tank, and shoot small round bullets at Polygons and other players to level up, and upgrade your tank in these 8 stats: After every level up through 2-28 you get a upgrade point to upgrade one of those stats from a menu like the one seen here. Then, every 3 levels 30-45 you get an upgrade point.
 * Health Regen
 * Max Health
 * Body Damage
 * Bullet Speed
 * Bullet Penetration
 * Bullet Damage
 * Reload
 * Movement SpeedThe_skill-tree.png

Controls
Although all you really need to play the game are WASD (or the arrow keys) to move and click to shoot, there are many other controls.
 * Moving: WASD/↑→↓← - W/↑ for up, A/← for left, S/↓ for down, D/→ for right.
 * Aim: Mouse - your tank will point toward your mouse.
 * Shoot: Click, or press space. Hold works too if you see clicking many times is annoying.
 * Drone Repel: Right click or Shift - drones from Overseer, Overlord, Manager, and Necromancer will move away from the mouse.
 * Upgrade: Either click the "+" button next to the stat you want to upgrade, or press the number key shown next to the upgrade.
 * Autofire: Press E to turn on Autofire - your tank will shoot continuously without the need to hold the mouse down. Press E again to turn Autofire off.
 * Maximize Stat: Pressing M and a number key will automatically place upgrade points as they become available into the stat corresponding to the number. Pressing M alone will cancel maximization.
 * Autospin: Press C to turn on Autospin - your tank will spin slowly, no matter what your mouse is doing. Press C again to turn Autospin off.
 * Full screen: Press F2
 * Open class tree: Hold Y to show the entire class tree (all the classes, and the path to get them). When you finished looking at it, release the Y key.

Classes
Diep.io also features some playable classes which can be activated at levels 15, 30, and 45 (max level). You start as a normal Tank with a singular gun which shoots a single bullet. Classes come in tiers.

Tier 1
Tier 1 tanks are:

Tank- One normal barrel on front. (nothing special)

Tier 2
Tier 2 tanks are:

Twin- Get an extra turret on your front, making you shoot 2 bullets in front instead of 1.

Sniper- Your map view is slightly increased, and you shoot less frequently, but you fire faster and more powerful bullets.

Machine Gun- Your gun turns into a trapezoid. You fire bullets more frequently, but inaccurately.

Flank Guard- You get an extra gun at your back, increasing coverage.

Tier 3
Tier 3 tanks are:

Triple Shot- From Twin. You now have 3 turrets in a scatter-shot position which fire bullets simultaneously.

Quad Tank- From either Twin or Flank Guard. You now have 4 turrets pointing at the cardinals and diagonals, which fire bullets simultaneously, increasing coverage even more, but decreases focus of fire.

Twin Flank- From either Twin or Flank Guard. You now have 4 turrets, 2 on the front and back, both of which fire like a Twin.

Hunter- From Sniper. You start shooting a small bullet, then a big bullet right after, both in front of you.

Assassin- From Sniper. Your map view becomes increased even more, and your bullets do even more damage.

Overseer- From Sniper. It shoots controllable drones which follow your mouse and last until they are destroyed. These drones are affected by Bullet speed, damage, and penetration, turning them into Drone speed, Drone damage, and Drone health, respectively.

Trapper- From Sniper. It places traps on the map and it harms whoever goes on them.

Gunner- From Machine Gun. Now has 4 small turrets which fire tiny bullets in a pattern. These bullets are the same as normal ones, but they are easier to penetrate.

Destroyer- From Machine Gun. You start firing huge cannonballs that have insanely high damage and penetration really slowly. Its recoil is quite high.

Tri Angle- From Flank Guard. You now have 2 guns which are branching out at your flank. Because of this, It can move really fast due to recoil physics.

Smasher- From Tank. You now lack a cannon, and the bullet-related stats disappear, but your remaining stats increase their max level (7 → 10). You have an hexagon shell behind your body that turns quickly. You have to use the Basic Tank until level 30 to get this class.

Tier 4
Tier 4 tanks are:

Penta Shot- From Triple Shot. You now have 5 turrets in front of you in a scatter-shot position that fire storms of bullets in a pattern. It is very hard to dodge once it targets you.

Triplet- From Triple Shot. You now have 3 turrets in front of you that are in a straight line, like a Twin with an extra turret. It fires a crazy amount of bullets in a straight line in front of you.

Spread Shot- From Triple Shot. You now have 11 turrets in front of you. The center turret shoots a Basic Tank bullet, and the other ones shoots Auto Tank bullets. Bullet Damage and Penetration are decreased. For some reason, this tank doesn't get recoil while firing.

Octo Tank- from Quad Tank. You are now completely surrounded with 8 turrets which fire in a pattern. Its coverage is ridiculous.

Sprayer- From Machine Gun. You now look like the Hunter, having a gun coming out of the trapezoid gun. When you shoot bullets the first bullet is smaller while the next one is bigger.

Triple Twin- From Twin Flank. You now have 3 sets of Twin turrets which still fire the same.

Predator - From Hunter. You now shoot 3 bullets- a small one, then a medium one, then a penetrating big one. You're also able to move your Field of View by using right click.

Streamliner - From Hunter. You now shoot 5 equally-sized bullets extremely fast, giving you the fastest Rate of fire of the Sniper branch. However, your Bullet Damage and Penetration are crippled.

Stalker- From Assassin. Quite the same as its predecessor, but can turn invisible when kept idle. Moving or shooting twice will turn you visible again.

Ranger- From Assassin. Your map view gets increased once more, and your bullets get extra speed and penetration.

Necromancer- From Overseer. Your tank turns into a square and touching the Yellow Squares around the map turns them into deadly, controllable minions which can be released by releasing the left-click. It turns the Reload stat into "Drone Count", which adds the number of square minions you can have.

Manager- From Overseer. Just the same as the Overseer itself, but can turn invisible like the Stalker. You won't turn visible if you spawn in your drones, unlike Stalker. It also spawns in drones half as fast.

Overlord- From Overseer. The amount of drones you can spawn at once with Overseer is doubled with this tier. Very good at anything but moving fast and defending itself easily.

Hybrid- From Destroyer. You get an extra drone spawner at your back with this tier, and you can summon 2 drones that protect you and auto-attacks anything near.

Fighter- From Tri Angle. A single turret appears on both sides of the Tri Angle, making it have extra coverage, but lower speed.

Booster- From Tri Angle. The 2 turrets at your back will now double, granting more flank defense. Prior to this, it is slower than the Tri Angle.

Mega Trapper - From Trapper. Traps deal more damage but are slower. Prior to this, it has less reload.

Tri-Trapper - From Trapper. Gains 2 more barrels, making it shoot in 3 directions at once. The traps don't last as long, however.

Gunner Trapper   - From Trapper. Gives it 2 Gunner barrels for defense.

Overtrapper - From Trapper and Overseer. Gives it 2 drones to defend itself.

Auto Trapper - Can shoot gunner bullets out of a auto cannon (used on auto gunner) and can shoot medium sized traps.

Other
Mothership- A level 140 tank available only in the Mothership gamemode with all stats maxed out except Health Regen, which has 1 upgrade point. It has 16 guns that spawn drones, up to 32 drones at once. Players swap control with it every 5 minutes.

Trivia

 * Many believe that .io is a game tag for multiplayer games. It is actually a domain in the British Indian Ocean Territory, where the British and the Chagossians take some of the profit from the people who use the .io domain. Since no Chagossians live in the area, and the British soon denied the profits from the domain, .io is a free domain.