Autoclicker

An autoclicker is a software program that automates the use of the mouse. There are several options available. A recommended one is Orphamiel OP Auto Clicker

Uses
The main use is to fight battles in the War Zone. Although for this you can also use the in-game autoclicker (see below).

For time challenges, an external autoclicker is a must. Again, unless upgraded in the command center (but there are better uses for your RP)

Also on invasions, unless you buy the one-click invasion upgrade in the Command Center (again, there are better uses for your RP)

An autoclicker is also useful (on a much longer timescale, a click every 10 seconds or so) to automate the buying of certain Units and/or Upgrades in the Boot Camp.

In-game
The game contains an autoclicker as well, in the War Zone, subject to certain limitations, which can be improved with Command Center upgrades.

The in-game autoclicker has both a clicks-per-second limit and a time limit. After the time is spent, there is a cooldown. After the cooldown, you have to manually activate it again. These limits can be improved on the command center
 * Cooldown 5s from 10s -> Level 15
 * Increases firing time to 60s -> Level 50
 * Increases rate of fire from 4/s to 6/s -> ??
 * Increases rate of fire from 4/s to 6/s -> ??

There is an unlimited autoclicker (10/s, no cooldown) available for 15.000 gold. There are periodic offers with a heavy discount (up to -70%, total 4500 gold). You should buy it if you find this offer.

A big advantage of the in-game autoclicker is you can leave it running on the background (very useful for those long grinds, when you kill an enemy every 1-2 clicks, and thus you may need up to 30 min to empty a full tank of fuel).

Limits
The developers warn that in order for external autoclickers to work with the game, they should be limited to a max. of 10 clicks/s, which is the game's limit.