Red Hat JBoss Fuse is an open source Enterprise Service Bus (ESB) that focuses on mediating, transforming, and routing data across multiple applications, services, or devices for both internal systems and external services. By implementing the Open Source Gateway initiative (OSGi) specification it allows bundles, or modules of functionality, to be loosely coupled and highly reusable; in addition, bundles may be remotely installed, started, stopped, updated, and uninstalled without rebooting, and multiple versions of each bundle may run simultaneously.
Though no canonical definition of an ESB exists, David Chappell states in his book Enterprise Server Bus,
An ESB is a standards-based integration platform that combines messaging, web services, data transformation, and intelligent routing to reliably connect and coordinate the interaction of significant numbers of diverse applications across extended enterprises with transactional integrity.
| ||--David A. Chapell|
An ESB simplifies the complexity of integration by providing a single, standards-based infrastructure into which applications can be plugged. Once plugged into the ESB, an application or service has access to all of the infrastructure services provided by the ESB and can access any other applications that are also plugged into the ESB. For example, you could plug a billing system based on JMS into an ESB and use the ESBs transport mediation features to expose the billing system over the Web using SOAP/HTTP. You could also route internal purchase orders directly into the billing system by plugging the Purchase Order system into the ESB.