Textile 2
Textile 2 is now available for testing, courtesy of Dean Allen. Textile is one of the more popular structured-text style markup languages, which translate a simple markup language in to HTML. What made the original Textile special was that it concentrated squarely on structural markup, providing intuitive shortcuts for most structural XHTML elements. Textile 2 takes this further, but also introduces a number of presentational effects such as block alignment. Beta PHP code is available in addition to the demo.
That said, the killer feature of Textile 2 in my opinion is the fact that it has been developed as a collaborative effort between Dean Allen and Brad Choate. Brad created a Perl port of the original Textile (Mark Pilgrim did the same thing for Python) but this time round they have been working together to define the format. If they are successful, Textile could become a useful mini-standard for authoring structural markup. At any rate, since Textile is intended to be a shorthand technique to complement HTML rather than replace it it is well worth a look.