I'm working on a server administration app for Android with Material design in mind.
App works with any Minecraft server (including vanilla, spigot etc.), using only RCON and Query (you have to enable both in your server.properties).
You can send most basic server and player commands and also custom commands.
App also supports some plugins and their commands (just PlugMan, NTheEndAgain and Multiverse-Core as of now).
If your server has Dynmap, it can also show Dynmap inside the app.
I have a fully functional app now and I'm offering you to become Alpha testers.
If you are interested, leave a message here or send me a Private message and I'll send you download link.