Nope, it's its own thing. It's federated, so you can view piefed content on lemmy and vice versa, but it's a separate platform built in a different language by someone else. I like it better mainly because the lemmy devs are transphobes who are fond of the idea of mass murdering their political opponents.

It’s a different software stack, both server and client. But it uses the same protocol as Lemmy for federation (same story with kbin/ mbin.) so all those talk to eachother.

Its a similar base but distinct in feature set and backend.