It's my custom layer to an C++ code editor "4coder". It's based on 4coder's default custom layer (written by Allen Webster).
The keybindings to a large extent are inspired by those in Vim.
Just drop custom directory and build.bat into 4coder's directory; then run build.bat. If you want to also compile the lexer, then run build_lexer_and_custom_layer.bat instead.