Apple has recently made a large commit to the SproutCore project on GitHub, which was stuck getting clearance from Apple's higher-ups for awhile. Here's a post from Charles Jolley briefly talking about their 1.0 march, dated 12/5/2008.
I haven't personally taken a look at what the changes in Bitburger (the name of Apple's branch) entail, so I'm not sure they're more geared towards developing an application like anything in iWork. Just food for thought.
Technology, design, and bacon lover. Software engineer in San Francisco, CA.