I <3 TextMate, and I <3 Markdown. I wanted a tool which allowed me to write Markdown in Textmate, and preview it in realtime in Google Chrome.
Install via rubygems
$ sudo gem install markdownie
In the console
$ markdownie <dir>
Markdownie will then look for markdown files in that directory, and generate an index which you can see by browsing to http://localhost:5678.
Every time you save the file, the updates will get sent to the browser.
Markdownie will look for a css folder in the folder you're watching. If you add a stylesheet named screen.css to it, it will take precedence over Markdownie's.
The MIT License
Copyright (c) 2010 Julio Cesar Ody
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.