Have you read the privacy contract ?
Because you should
https://mastodon.social/terms

See the fedivers for hundreds of instances of gnu social (what mastodon runs on)
http://www.fediverse.org/

If you want to install one on your server here's the manual
https://karp.id.au/social/en/admin/index.html

Beware of datamining
https://media.ccc.de/v/33c3-8414-corporate_surveillance_digital_tracking_big_data_privacy