rendr 2
I saw Max Kiesler's mHub blog post about this amazing html/css prototyping tool the other day. WOW! It's called render 2 and it's a great tool quickly double checking some code and seeing what it will look like with realtime changes. Perfect for web designers wanting to work out color combos, size issues, etc. As you type the sample page changes, INSTANTLY! No waiting for it to update or anything. Not only is it a good useful tool, but it's just plain fun!
