The Open Services Gateway Initiative (OSGi) may seem like yet another darn spec about yet something else computerdom can't live without, but this one seems to be pretty important and catching on. As I understand it, the OSGi spec defines a component model with two main capabilities:

• bundles -- Equivalent to Eclipse plug-ins, a component of code with a defined API that provides specific functionality.
• services gateway architecture -- Makes the bundles accessible as services.

Here's the description of OSGi on developerWorks:
OSGi is a set of Java-based APIs to implement a services gateway architecture. This services gateway is inserted between the external network and internal network and devices and will aid the delivery of managed broadband services to networks in homes, cars and other environments.
The OSGi FAQ helps explain what the spec is about.

(Original blog posting: OSGi, the Eclipse Platform, and SOA)