[marttt]

Rob Pike's acme text editor for the Plan 9 operating system: http://acme.cat-v.org/

https://www.youtube.com/watch?v=dP1xVpMPn8M (excellent overview of the editor by Russ Cox)

And acme's predecessor sam: http://sam.cat-v.org

You'll need plan9port to run acme on Linux, though. But the core ideas are very simple and powerful (sam: everything is a huge string; acme: everything is a clickable file) and thus hopefully long-lasting.

I would also mention edbrowse, a line-oriented web browser initially for blind people. Maybe this is too far on the fringe, though. It does have a lot of depth (excellent scripting capabilities); it's an amazing project actually: http://edbrowse.org/