This is a bit of a work in-progress, but for the most part I like what I have done here.
I switched to Dvorak some time ago and software-based support in most OS's for Dvorak isn't very great, so this keymap by default is set to Dvorak.
This layer gets toggled off and on to place a numpad on both the left and right sides of the keyboard.
This layer holds some handy shortcuts that I use often, like the screen grab shortcut and sleep shortcut in OS X.
It also has quick access to {} as they are inaccessible in the base layer
Aside from quick access to [] and Play/Pause/Next/Previous, this layer is mostly just goofy things I decided to program into the keyboard because I could. There's a bunch of kaomoji/"unicode smileys" and I added a toggle switch to enable a Zalgo Text mode.
This layer is a "here be dragons" layer. It can only be accessed by holding down the keys for Lower and Raise at the same time. I added exclusively keys that drastically transformed the keyboard's layout or function on this layer. The ability to switch to Qwerty is on this layer, a way to switch CTRL and CMD back and forth is on this layer, and a hotkey to enter bootloader mode also exists.