JGroups is a very mature project (it exists since 1999) authored by Bela Ban. It continues to have a very good support from the development community. It serves as a foundation for several projects such as JBoss application server and related components such as Jetty Http Session Replication, Tomcat HTTP session replication, among others.
JGroups has many useful features, but the most important is the reliability. It takes the standard protocol such as TCP and UDP and includes additional features to improve reliability and failure detection. The features are: