Today I tested Pocketmine-PE. It's a Multiplatform server for Minecraft PE. My test system was running lubuntu 15.04 x64.
Following the instructions on the download screen to add the requisite libraries, dump it to the hard drive and get it up and running was dead easy. After having a quick play with the config files I connected to it with my tablet without an issue. It appeared on the world screen straight off.
The world generated looked serviceable. Because I was trying the beta and not the new alpha it lacked booked and a few other features but the world was reminiscent of perhaps PC alpha 1.6. It lacked biomes and caves but was quite playable.
Doing basic tasks like digging, punching a tree, using a crafting table and a furnace worked alright. There seemed to be a slight issue with crafting where it didn't always stick but repeating it would work.
It doesn't have mobs implemented yet, but it does use the network message system to display achievements analogous to Minecraft on PC and console.
The website offers a large number of plugins for Pocketmine-PE. I haven't tried these yet but I believe that if the server gets developed further it could be a real killer app. Having Craftbukkit like functionality for a mobile platform could really help give Minecraft PE a boost for players that prefer a less casual gaming experience more in line with modded servers.
In short it's not ready for primetime if you want a survival mode experience but would work fine for collaborative creative mode action.