I've talked about the WebSphere Software Early Programs. Those are for all WebSphere products, including stuff like our Java 6 SDK, but only for feature packs that are in early release (alpha, beta, etc.). There are feature packs that aren't one of the programs any more because they're now GA (generally available).
For the list of all WAS 6.1 feature packs, both early programs and GA, see WebSphere Application Server Feature Packs. It currently lists four of them:
- IBM WebSphere Application Server V6.1 Feature Pack for Web Services (GA) -- discussed in MTOM/XOP in WebSphere
- IBM WebSphere Application Server V6.1 Feature Pack for SOA (Beta) -- discussed in Overview of SOA Feature Pack for WAS 6.1
- Ajax for IBM WebSphere Platform (Early Program) -- discussed in Ajax for IBM WebSphere Platform
- IBM WebSphere Application Server Version 6.1 Feature Pack for EJB 3 (Beta) -- discussed in WAS 6.1 Feature Pack for EJB 3
The beauty of these feature packs is that they give you functionality that's newer than WAS 6.1 without having to wait for the next release of WAS. For example, WAS now has support for MTOM and XOP, which is newer than WAS 6.1 and normally otherwise wouldn't be available until the next release. Also, by making them available as betas/previews, you're able to try them out, report bugs, and request enhancements while there's still time for development to fix and improve them. Who knew IBM could be so responsive?