You may also have a look at The Universal MUMPS(M) commander (Alt-NC) (http://minimdb.com/tools/altnc412.html).
It is similar to other commanders well known outside of Caché/M communities, such as Midnight Commander (mc, Linux), File and Archive Manager (far.exe, MS Windows), and of course their predecessor famous Norton Commander (nc, MS DOS) in many ways. Full screen editor which is included into commander is very simple and easy to learn. It is not so sophisticated as great programmers' tools of the past (such as DEC's EDT), but a bit smarter than notepad (MS Windows) as it is full functional without a mouse.
Pros: it runs from a command line, it does't force any extra tcp port to be opened, it supports as much terminal types as OS does, it has a non-% version so you don't need CACHESYS:RW privilege to load the code.
Cons: the screen design is pretty ancient, but should we expect too much from CHUI application which roots come from early 1990x?