S1AS is a commercially development of the J2EE Reference Implementation (RI) along with iPlanet AS 6.x features. It's supported for production use, unlike the RI, more complex in its user features, and ties in to Sun's
IDE very nicely. This makes the whole tool more like WebLogic and WebSphere, which dominate the commercial market.
I've taught support readiness training to Sun's tech support people on S1AS SE; there's a lot more in this product than the RI, in particular administrative control features, an embedded web server, and more. Most iPlanet AS 6.x services are includedor fused with J2EE; vestiges of the old Kiva stuff, like the C++ interface and the multi-process controller architecture, have been cleaned up and unified a great deal.
S1AS comes with the second major release of Solaris 9 media too, to help distribute the product widely. As a key component of Sun ONE, they naturally want everyone they can reach to try it.
[ November 17, 2002: Message edited by: Michael Ernest ]