My software is like an on-screen keyboard with context-sensitive prediction, more sensible orientation and layout, and lots of shortcuts overloaded on the buttons, operated by the other mouse buttons and the scroll-wheel. So, for example, moving a word/page at a time, selecting lines/files, unindenting, etc. are just done by scrolling in the right place, control-A is middle-clicking A, and so on (the program just sends the appropriate keystrokes to make things happen). Selecting and toolbars/menus are fast because you're already using the mouse, and copy and paste is just select and middle click on Linux.
RSI basically forced me to develop the system (I can't use a physical keyboard, and no existing software was or is good enough), and I have been using it for all my typing since 2003. I'm now working on making a commercial version aimed primarily at touch screens (gestures will replace different mouse buttons).
I'm not sure that there's much more to it than what I've already described. I think what it's got going for it is refinement driven by nine years of dogfooding day in day out, and that refinement isn't easy to describe as it's just many tiny little choices.