The question has come up several times in the irc the last few days, as to how to use the Sproutcore master branch. Peter Wagenet keeps answering it, and i figured it would be helpful to write it down.
The following is currently only working on Ruby 1.9.2. The easiest way to set that up is to use rvm.
gem install bundlerif you don't have it
gem 'sproutcore', '1.5.0.pre.3'
bundle install --binstubs
Windows also needs to add
gem 'eventmachine', :git => 'git://github.com/eventmachine/eventmachine' because otherwise it won't compile