PieFed communicates with Lemmy. Same content, different platform. That’s one awesome thing about federation.
There is also mbin (fork of kbin), and Sublinks, which is API compatible with Lemmy so should be able to use Lemmy apps with it (from memory, this is what Beehaw are hoping to move to).
Pretty sure that’s a plus subscription for if you want to support them. It gives you hourly map updates and weather and other stuff hardly anyone needs. But you can use the app fine without it.
I still prefer Organic Maps though.