This server is called PlanetNostalgia and it runs Minecraft Alpha 1.1.2_01. It is trying really hard to feel like Minecraft back in 2010 with the bright green grass and the old terrain and the simple kind of gameplay.
The server has chest furnace and land protection so people can actually build and keep their stuff safe. There are PvE fixes using something called the MixxitPlugin. It also has an economy and shops so you can trade and buy things instead of just grinding everything alone.
They use grief and cheat protection so the world does not get wrecked by people who just want to ruin stuff. It also runs on custom server software and they say it is stable and not laggy.
PlanetNostalgia is all about keeping the original Alpha feeling but still accepting that the old game had some frustrations. The idea is to make it feel like the golden era of Minecraft again and let both old players and new players see what that version was like.
