It's definitely not pretty (yet) but it is working and that is what is important. Clients can connect and move around the world together. I finished chunk synchronization which required a whole queue system and some other complicated business.
Real-time chunk updates are working as well so if a client changes a terrain tile, other users will see the changes instantly.
Tested Over The Internet
I ran a few tests over the internet (thanks to Panos and Seb) and was surprised to see no issues occurred even with low bandwidth download speeds. Of course I won't really know until the multiplayer is more 'functional' how efficient it is but for now I am more than satisfied.
World sync is functional at last! Everything seems to be sliding along smooth as butter. Without any fear I go onward towards the next steps of developing the multiplayer!
Terrain tile data is now kept inside of chunk files instead of being compressed in all together in a separate file. This means faster reading/writing and larger worlds! World is 256x256? Not a problem! Same save and load speeds as any other size world. Pretty neat huh?
Keep Petting The Dog
World generation is functional and even cross-compatible with the singleplayer. That means you can take a singleplayer world into multiplayer and back if you wanted to! Aside from that lovely feature the world generation is VERY fast. As you can see below... The speeds will vary based on the biome mod files used of course but they will likely never go beyond 5ms per chunk.
The server is also VERY capable in terms of world capacity. I would be blown away if a server could fit more clients than required world space onto a server. Assuming clients aren't too heavy for a server I would expect to see servers that are 512x512 chunks running on low end machines such as tablets.
I also setup mod verification for client to server connection. What this means is that users who modify a mod pack will be unable to connect to a server that doesn't have the exact same files. Even a single number changed will result in a mod mismatch error. This is just a first step in anti-cheat for Project Explore but a big one nonetheless. This is not to say there aren't workarounds but this will definitely prevent easy cheating.
Lastly I implemented a new server command! kick_user which can be used to well... kick users of course! It is already working perfectly which is a good sign.
I hope that things keep moving at this rate. If they do I just might have multiplayer up and running for users in the next stable build. However I can make no promises!