So the cool part about Mastodon, right? You don't need to be on the same domain as other people to talk to them. You can sign-up on or invite your friends to:
mastodon.madrid
mastodon.cat
mastodon.eus
And many others, and still be able to talk to the world / follow your friends on mastodon.social and vice versa.
Please help those servers grow by spreading the word about them! (And if you are interested in starting a new server, you can do that too!)
@Gargron Hey Eugen, it's mastodont.cat not mastodon