1.8.8 ((new)): Eaglercraft

This is the most common question.

Here is a deep dive into why Eaglercraft 1.8.8 became such a solid staple for the community, how it worked, and where it stands today. eaglercraft 1.8.8

Eaglercraft was different. It was a "web port" of the reverse-engineered Minecraft 1.8.8 source code (specifically based on the Bukkit project and other open-source reverse-engineering efforts). This is the most common question