Imagine if you combined Garry's mod with Minecraft, only better. This game will have an in-game editor, so you can make changes on the fly, and have your players see them immediately. Need some trees? Just open the editor, draw a quick texture, make a new block type, and voala: Trees. No need to send .mod files or restart the server, everyone already has your changes.
Code editor is fully functional, with errors for that file shown at the bottom. An error icon will show up for faulty code files in the Package Explorer. You can also set a startup package. There is a right click menu for packages too, you can rename and add new items there (and set the startup package).