I like to putter around on Minecraft now and then, and I’ve been using a free (well, they do ask for small donations once a year) public server called Sitosis. Did you see me write free right there? That’s what makes it shocking that it is woefully underpopulated right now, so they’re open to new applications. There’s a gigantic world there waiting to be played with, and we’ve only developed a tiny bit. Here’s the island a couple of us have been tinkering with lately.
One other reason that it might be less than packed with people is that it really is a totally vanilla server in survival mode — no hacks or mods. They also expect players to be mature and respectful of one another, so no griefing or screwing around with others’ enjoyment of the game. They also occasionally reboot everything and start fresh, but that’s only done by vote of the users.
There might be a few other Minecraft tinkerers here, so signing up a few more might get the place hopping again.