It exists, it's called GridCoin. It's a proof of stake chain that disburses coins based on work units completed on the Berkeley Open Infrastructure for Network

It exists, it's called GridCoin. It's a proof of stake chain that disburses coins based on work units completed on the Berkeley Open Infrastructure for Network Computing (BOINC). There's a few others that take different approaches like Golem Network Token, Nym, Oxen, etc.