the "everything is a file" metaphor
Frankly I never got it until recently. Sure, I had some informal contacts with plan 9, the OS that is entirely designed around that concept. First when Linus talked about the features he borrowed for Linux, later I borrowed myself features from Plan 9's editor acme for Kephra. But yesterday I saw a talk from the author of MacFuse and I really got a hang of it.
And suddenly I realized the implications for a better Kephra that I currently design. When it read and writes FIles it should have hooks to do whatever (aka *). Not only be able to write files on remote machines via ftp/sftp/*. But also use it to literally edit *. I mean, why do I have to use the clunky Wiki editors, when I can have Kephra, where I'm twice as fast and can store the relevant parts of everything i write in the right places for later reuse? Even that box i currently typing in sucks compared to any decent editor. And please with the right module (Mechanize and friends) its a handful lines to do that.
I really enjoy this (4th or 5th) rewrite.