Abstract: A system (100) produces complex multimedia contents by an author for a user. The contents include a base content and additional content associated and synchronised with the base content. An editing subsystem (101) includes a software platform and hardware supporting the software platform. An event editor allows selecting additional content and synchronising to produce a complex multimedia content synchronised relative to an actual time evolution of the base content. The additional content represents an event associated and synchronised with the base content. A back-end subsystem (102) includes a database (103) storing the complex multimedia content produced by the editing subsystem for making the additional content available. A front-end subsystem (104) has a software platform and hardware supporting the software platform. The front-end subsystem (104) software includes an event engine loadable to a client device (105, 115) to enable using additional content simultaneously with base content.