wee is a rubyforge project that mostly implements the ideas in the smalltalk project seaside2. The interesting part, which i havent completely figured out, is the back button actually rewinds the state of the webapp.
wee comes with a demo widget that is an integer incrementer. put two on the same page. increment one to 2 and one to 3. then increment 3 to 4. go back one page - the counters read 2 and 3. increment 2 to 3. in most web apps, the result would be 3 and 4 but in wee, the next page shows 3 and 3.