By alexismp on Jan 14, 2011
Weld is the CDI reference implementation and Seam is a JBoss-sponsored community effort to build modular extensions for Java EE 6. Seam targets standard Java EE runtimes and other environments where CDI is integrated. There's recently been a focus on compatibility, specifically to get Seam 3 running smoothly on GlassFish 3.1. You can read more on Seam 3 in this post by Dan Allen.
On a related note the upcoming GlassFish 3.1 will integrate Weld 1.1 Final as previously mentioned. This should remove the vast majority of CDI problems found in 3.0.1.