JRun is an application server from Macromedia that is based on Sun Microsystems' Java 2 Platform, Enterprise Edition (J2EE). JRun consists of Java Server Page (JSP), Java servlets, Enterprise JavaBeans, the Java Transaction Service (JTS), and the Java Messaging Service (JMS). JRun works with the most popular Web servers including Apache, Microsoft's Internet Information Server (IIS), and any other Web server that supports Internet Server Application Program Interface (ISAPI) or the Web's common gateway interface (CGI).
JRun comes in four editions: Developer, Professional, Advanced, and Enterprise. The Developer Edition consists of the full JRun package, but it is licensed for development use only and is limited to three concurrent connections. The Advanced Edition is designed for deploying JSP and servlet applications in a clustered server environment. Companies who host servlet and JSP-based Web applications from a single server use the Professional Edition. Companies who build and deploy e-commerce Java applications use the Enterprise Edition.