Fast lightweight espionage probe.
Observers are super fast units that travel five times faster than the next most fastest unit. They are cheap and quick to build and are perfect for Explorations.
Their capacity is extremely low, as well as their combat stats, which makes them a useless unit for Raids. Although some players use them as distractions (fodder) to make enemy units target them and spare other units since they are cheap and quick to build.
Observers are a vital unit for Intelligence since they (temporarily) boost your Intelligence Level by 1.