In the Star Wars universe, astromech droids, or astro-droid, were small utility robots usually used for such tasks as battle mechanics, or just simple maintenance robots. R2-D2 a famous astro-droid, property of Jedi Master Luke Skywalker, is of the revolutionary R-series.
Astro-droids were first built when the Old Republic, hungry for power, hired Industrial Automaton to build them a "droid of all trades." Industrial Automaton's first attempt at this was the P-series which, although successful, was not enough. The R-series was built with several built-in tools such as carbon filtered jets, computer terminal outlets, and others for ship repair.
The Rebel Alliance often used R2 units to increase the hyperspace range of their snubfighters and to preform in-flight repairs.