Directly compatible with Lemmy, there's Friendica (Facebook-like; also compatible with Twitter-like posts e.g. from Mastodon), Mbin (simplified/cleaner UI; also hybrid like Friendica), and PieFed (apparently more Reddit-like than Lemmy from what I read, in a technical sense).
Dunno which are better/worse to run, but I remember seeing hardware requirements on the docs of each of them.
Also it's not uncommon to see single user instances from my experience. But if you feel it's a waste of domain/resources, you could also create some dedicated community or something to give further use for it.