An oldie but a goodie, this was a project I did in freshman year of high school, and the first time I made a level editor.
The only computer class that my high school offered used visual basic via Dark Basic (which it looks like might have been open sourced?) which was a simple windows game engine. Having some previous programming experience from making games of my own I was bored out of my mind and decided to take matters into my own hands.
At this time I was working on an adaption of the Minecraft mini game spleef where players would try to dig away blocks to make their opponents fall. Making/editing levels was a real pain as I would simply place the blocks in my 3D editor, so I figured it would be a great project to sneak into class!
The editor offers:
Rudimentary file saving and loading (via a simple ascii format)
Zoom levels (Multiple!!)
Optional mirroring that you could turn on and off on a per axis basis
Onion skinning so you can see the layer below the one you’re looking at.
There were some serious problems: to load a file you had to have it correctly named in the same folder as the application, and the more blocks you had on screen at once the slower it ran (each was a separate draw call from the CPU…). Even with all it’s problems, I was, and still am quite proud of what I was able to do!