For example STEPS a full modern computing environment in 20KLOC from the metal up using DSLs and a reimagining of what an OS and the Web means.
Some more Info here: "STEPS 2011 Progress Report (personal computing in 20kLOC)" http://lambda-the-ultimate.org/node/4436
"Alan Kay: How Simply and Understandably Could The "Personal Computing Experience" Be Programmed?" http://vimeo.com/10260548
"Programming and Scaling" http://www.tele-task.de/archive/lecture/overview/5819/