To create a server for Minecraft PE Alpha, you can use older versions of PocketMine, or you can use NostalgiaCore, a fork of the old PocketMine that has many fixes and new content.
We recommend using NostalgiaCore, as it has PocketMine bug fixes, as well as new features, for example, mobs with AI, working reactor of the lower world, rails, etc.
NostalgiaCore is available for versions 0.8, 0.9, 0.10 as well as 0.7 and 0.6 (these two versions are abandoned)
Download old PocketMine here: https://legacyminecraftpe.github.io/LegacyCoreVersions/
Download NostalgiaCore here: https://github.com/kotyaralih/NostalgiaCore
You can download the PocketMine installer for Windows, and after unpacking the server files replace PocketMine's src with NostalgiaCore's src.