Of course this service is free of cost to use - but it is not free of cost to operate and to offer it to you.
Supporting this service voluntarily by some small amount of money helps to provide this service as it is now.
Please remember that the #fediverse mostly consists of people that are committing their spare time and personal money to provide others with a free service.
On Twitter, on the other hand, you have adds and your data is being sold to other company. But not here.
All friendly creatures are welcome. Be excellent to each other, sei humanistisch, keine Nazis, keine Hassrede. Nicht nur für Nerds, aber die Domain ist irgendwie cool. ;) Keine Bots im Allgemeinen erlaubt! (nur mit vorheriger Genehmigung). Sprache ist hier hauptsächlich Deutsch, Englisch auch erlaubt. --- All friendly creatures are welcome. Be excellent to each other, live humanism, no nazis, no hate speech. Not only for nerds, but the domain is somewhat cool. ;) No bots in general! (only with prior permission). Main language is German, English is allowed.