The GURPS second edition tech manual had T9 (fusion age) energy grenades that were not technically one-shot devices unless you dialed them to specific settings. IIRC they had to be recharged after every use regardless, but unless you selected the "it's got to go" option when throwing them your grenade could be recovered and reused.

Other game systems, which makes combat more abstract, do essentially have unlimited grenades, an example would be the Cypher system (Numenera, the Strange, and a handful of generics) where something as -- mundane, as simple explosive ordinance isn't worth tracking on an item to item basis in most cases.