It's amazing how fast it's growing. According to Lemmy Explorer, there are nearly 900 Instances, encompassing almost 13,000 communities. The forum software could stand some improvement, like having a way to group all your communities in one place, or figuring out whether an instance is federated. I really like the decentralized aspect of it. If a corporation tries to take over and ruin the largest instance (like what's happening to Reddit), then folks can migrate over the the second-most popular instance(s) while the biggest one withers and dies.

Also, Mastodon looks like a great replacement for Twitter.