As David touched on above, and we cover some in the recent SAFE Crossroads episode, PARSEC is just the algorithm and code that handles consensus on ordering of transactions/events. General formation and function of the network, security, connection, etc., is handled elsewhere than PARSEC.
Other decentralized systems could use PARSEC within whatever system they have or evolve. Also as David said, since SAFE is open source, other projects can take other parts and do with it what they find useful, but PARSEC is a specific function. It’s the difference between a consensus algorithm (or recipe?) and a consensus mechanism (close group, disjoint section).