I was inspired by the aesthetic of Besiege as you can see from the vignette background and the flat toolbars. I spent last night writing a toolbar GUI because I just wanted to get rid of the half broken toolbar I was using.
A floating tile information balloon hovers next to your mouse cursor to tell you exactly what is in that tile. Right now it doesn't count entities but it will. It even breaks the tile information into its 4 separate layers so you can easily tell what tiles are behind others and which layer you will be removing if you're in erase mode.
The tiles window is still there but eventually all tiles and entities and stuff will go in the bottom toolbar area and will change when you switch layers. (I actually wrote a windowing system for fun just to make movable toolbars. One of them was an Info window that contained the information the balloon does now. Will be a shame to get rid of it but it just doesn't work with my aesthetic anymore.)
Good UI design is really difficult. I've studied the editor UI's of a few games, mainly Besiege, to see what works and what goes where. I originally wanted one toolbar with everything so the editor area isn't crowded but eventually settled for a separate file toolbar and edit toolbar. I am also very intrigued by the UI of Super Mario Maker. It's so intuitive and awesome looking. While I won't be able to mimic everything, I might incorporate some features from it. Like the entity/tile chooser. Maybe you'll be able to choose favorites or it'll count which tiles and entities you use most and add them to a hot list in the main toolbar with a toggle to show all available entities and tiles.
Right now the game has 5 different types of layers per map. Collision, tiles, entities, coins and start/warp exit points. I plan on merging coins and start points into the Entities layer. Trying to simplify things. Believe me, it used to be more convoluted. I had layers for everything including separate plant, ladder, door and liquid layers. Eventually I made them all into entities. It's just a matter of time before I do the same for coins and start points. Start points can be merged with doors and coins will be an entity when I create an "entity painting" mode and easy way to delete multiple entities at once via a selection box. Also, it's really hard to think of an icon for the "Entity" layer. So I always end up just using an E. Hopefully the Collision icon (The overlapping squares) and the Tiles icon (The selected layer that looks like a SMB ground tile) are recognizable enough to work.
I'm putting more work in my editor than the engine right now.
I also have a neat entity filter in place that I'm proud of. It's animated and awesome and works like this:
