From the github page:
You can write HTML in a CSS-like syntax, and have Sparkup handle the expansion to full HTML code. It is meant to help you write long HTML blocks in your text editor by letting you type less characters than needed.
Sparkup is written in Python, and requires Python 2.5 or newer (2.5 is preinstalled in Mac OS X Leopard). Sparkup also offers intregration into common text editors. Support for VIM and TextMate are currently included.
He even included a video demo: