JOpenID is an OpenID 2.0 Java 5 implementation for OpenID sign on.

JOpenID is a very lightweight implementation for OpenID 2.0, about 50KB including source & binary.

JOpenID only needs JDK 1.5 (or above) and Servlet 2.3 (or above).

JOpenID is free, with Apache License.

JOpenID is very simple to use. See Wiki for more details.

JOpenID is now in the list of Java libraries on openid.net. You can download or use it in Maven.