GoBots were small robots (usually in the neighborhood of 3 inches) that changed into vehicles. Initially marketed in Japan as "Machine Robots," they were later spread to other countries under the "GoBot" moniker. They featured die-cast parts as well as plastic parts. They were marketed in Japan by Ban Dai and in other countries by Tonka.
Go Bots came out shortly after "The Transformers" came out and were never really able to compete with the larger toys. Later on, larger GoBots (or Super GoBots) were released that were twice the size of their smaller counterparts. A combiner was also released (Puzzler) as well as three different Power Suit sets (five separate suits that would hold a GoBot and can further be combined into a larger robot).
In the US, Tonka released several original toys (I think they were called Boomers) and featured a pop-up mechanism that would lauch a plastic ball. GoBots also had their own cartoon show. The leader of the good guys was Leader-1 and the leader of the bad guys was Cy-Kill. A spin-off line known as "Rock Lords" (where the robots would change into rocks) came later on.