@fuxoft I consider to run my own server in the future (one my project will probably violate rules of all current existing mastodon servers).
Based on my quick review, mastodon is resource demanding server even I need it just for a few members.
But - as I understand - you don't need exactly mastodon. You need any sw compatible with ActivityPub protocol.
Check https://fediverse.party/en/miscellaneous/ and select just ActivityPub in filter.
There are some pretty lightweight implementations (unfortunately for you - nothing in Lua :) ).
Pleroma looks promising for me (besides PgSQL installation, why!?!?! sqlite should be enough).