mastodon.social is one of the many independent Mastodon servers you can use to participate in the fediverse.
The original server operated by the Mastodon gGmbH non-profit

Administered by:

Server stats:

373K
active users

We've been hit by a massive DDoS attack. The site may not work as expected. We're working on mitigating the attack. Fastly are helping us. If in doubt, check status.mastodon.social for information.

Everything is back to normal now. Yes, it was an attack, not legitimate traffic. No, we don't know who was behind it. I agree the timing with Twitter being down was unfortunate.