Hi Brancliff! I'm glad you enjoyed the game!
This is a HTML5 game, so it uses the <canvas> element and JavaScript to run directly in your browser. I made it using the programming language Haxe (compiled to JavaScript) and the renderer Pixi.JS. If you're interested, see the credits for a full list of libraries.
The upcoming (expanded) Steam version will be downloadable, but I'll think about uploading a downloadable version of the free (and/or expanded) version here as well. Possibly with the next update. :)
I don't have any plans for a level editor right now (custom maps will be possible as mods in the Steam version, though), but maybe in the future!