From a technical standpoint, Radicle (P2P git protocol) is not related to $RAD.

$RAD is the token of the organization that has been funding Radicle over the years.

If the RAD token has nothing to do with their product, why does it have value? Did/do they have some other product that uses the token?

There is governance value in the token. Whoever holds that token can vote on Radworks governance proposals.