A lot of different stuff, but the things I depend on the most for actual work and direct OSS offshoots:<p>Snow Leopard, Ubuntu server &#38; VMs, XP VM (using VirtualBox)<p>Ruby, Haskell, Python, Javascript<p>TextMate, vim<p>git, gitx, git gui, vcprompt<p>bash<p>homebrew<p>postgresql, pgadmin<p>rvm<p>jquery<p>sass, compass<p>gemcutter, github<p>linode<p>chef<p>google apps<p>photoshop, illustrator<p>Firefox w/ firebug, firecookie, firequery, firerainbow, the web developer toolbar, cookie culler, user agent switcher, live http headers; webkit nightly dev tools; iPhone simulator from the iPhone SDK