The META/L editor is a direct assembly language editor. It shares some features of a Monitor program, with extensive use of metadata to take it well beyond anything a Monitor can do.
Unlike a text editor that later compiles your code, META/L interprets it as assembly language opcodes as you type it. Unlike a Monitor, you can do things like copy and paste code, move it around, or insert or delete bytes in the middle of your code; the metadata allows the editor to adjust parameters as labels move. Every byte of RAM and ROM is accessible to you on the fly.
Download the zip file, unzip it somewhere, and copy everything into the same folder as your r41 emulator. Full documentation is in the file docs/edit.html
This software is released under an MIT license.
There are also a number of videos in the forum here