mastodon.acm.org is one of the many independent Mastodon servers you can use to participate in the fediverse.
This server is generally intended to provide a trustworthy space for computing professionals from around the world to connect and engage with each other in a meaningful way.

Server stats:

231
active users

FYI, the Fedi spam problem is only starting out. It won't take much effort for someone to write a payload running on random compromised webservers to send copious amounts of spam via activitypub, making blocklists ineffective.

We will basically need to implement all the same anti-abuse stuff we're already doing for email in order to cope with it on the fediverse -- greylisting, dnsbl, domain authentication, etc.

Sadly, the only way this won't happen is if ActivityPub stays sufficiently niche to make other targets more popular for spammers.