TextMate Live Preview of GFM (GitHub flavored Markdown)
github-flavored-markdown, textmate, textmatebundles
Solution
Yes, it's possible to make a preview without file saving, just run `Bundles > Markdown Redcarpet > Preview` or here is a shortcut for this: ⌃+⌥+⌘+P.
To use a keyboard shortcut properly, I recommend to uninstall original `Markdown` bundle.
Problem
I found TextMate support for GitHub flavored Markdown http://github.github.com/github-flavored-markdown/ and now try to install (lots of ruby stuff needs to be installed, struggling..) then will try to have live preview feature. Perhaps, it is possible with a shortcut key, but is it possible on every modification without saving the file?