Glory games have released a free ruleset called Warbots.
From their announcement:
I’m celebrating the new year by releasing another free set of rules from the vault. This is an earlier design of mine — a quick, easy miniatures game for use with the MicroMachines Z-Bots, or any other toy robots you might have.
I was always a big fan of Comedy Central’s “Battlebots,” and fondly remembered “Rivets,” the old Fighting Robots boardgame from Metagaming. A decade ago, when I came across a bunch of Z-bots for sale, I decided to come up with a short set of rules for them that captured the fun mayhem of cute robots destroying each other.
“Warbots” fits that bill. You can download the rules, player sheets and 16 sample warbots.