BuSpar etc. (buspirone) is an anti-anxiety medication which is not chemically or pharmacologically related to other anti-anxiety drugs. Unlike the benzodiazepines, Buspirone has no anticonvulsant or muscle relaxant properties. It also lacks the strong sedative effect that is associated with more typical anti-anxiety (anxiolytic) medications.
Although it's not exactly understood how Buspirone works, it is known that it doesn't affect GABA receptors like the benzodiazepine medications. As a serotonin imbalance may be one of the causes of generalized anxiety disorder, BuSpar is thought to work by bringing levels of this brain neurotransmitter back to normal.