First, JavaScript Framework
http://prototype.conio.net/
Second, Ruby on Rails
http://www.rubyonrails.com/
Third, Script.aculo.us
http://script.aculo.us/
Fourth, Rico
http://openrico.org/
Five, Behaviour
http://www.ripcord.co.nz/behaviour/
Sixth, Sajax
http://www.modernmethod.com/sajax/