System for producing complex multimedia contents by an author and for use of such complex multimedia contents by a user, the complex multimedia contents comprising a base content and at least one additional content associated and synchronised relative to the base content, the system comprising: - an editing subsystem, comprising a software platform and hardware adapted to support the software platform, the software platform comprising an event editor configured to allow an author to select from a database said at least one additional content and synchronise it in relation to the base content to design a temporal execution of a user experience and produce a complex multimedia content wherein said at least one additional content is specifically synchronised relative to an actual time evolution of the base content, the additional content being intended, in the use of the base content by the user, to represent an event associated with and synchronised with the base content; and - a back-end subsystem comprising a database adapted to store the aforesaid complex multimedia content produced by the editing subsystem to make said additional content available to said user; and - a front-end subsystem, comprising a software platform and hardware adapted to support the software platform, the software platform of the front-end subsystem comprising an event engine adapted to interact with the back-end subsystem to allow the user to use the additional content simultaneously with use of said base content, the event engine being loadable by said front-end subsystem into a client device (105,115) of the user to enable said user to use via web the additional content simultaneously to said base content by means of said client device (105,115); wherein: - the editing subsystem is configured to store the complex multimedia contents to data structures adapted to store the information relative to the association of the base content with the additional content, including the synchronisation information of the additional content relative to the time evolution of the base content; - the front-end system is configured for loading a complex content from the back-end subsystem generating web pages and sending them to the client device together with the event engine; - the event engine is configured for being loaded in a user's browser and, once playing of the user experience has commenced, for extracting events from the complex content and dynamically activating various multimedia components according to time cadences established by the author with the editing sub-system; - the event engine is adapted to activate web applications in the client device (105, 115) allowing user interaction. - an editing subsystem, comprising a software platform and hardware adapted to support the software platform, the software platform comprising an event editor configured to allow an author to select from a database said at least one additional content and synchronise it in relation to the base content to design a temporal execution of a user experience and produce a complex multimedia content wherein said at least one additional content is specifically synchronised relative to an actual time evolution of the base content, the additional content being intended, in the use of the base content by the user, to represent an event associated with and synchronised with the base content; and - a back-end subsystem comprising a database adapted to store the aforesaid complex multimedia content produced by the editing subsystem to make said additional content available to said user; and - a front-end subsystem, comprising a software platform and hardware adapted to support the software platform, the software platform of the front-end subsystem comprising an event engine adapted to interact with the back-end subsystem to allow the user to use the additional content simultaneously with use of said base content, the event engine being loadable by said front-end subsystem into a client device (105,115) of the user to enable said user to use via web the additional content simultaneously to said base content by means of said client device (105,115); - the editing subsystem is configured to store the complex multimedia contents to data structures adapted to store the information relative to the association of the base content with the additional content, including the synchronisation information of the additional content relative to the time evolution of the base content; - the front-end system is configured for loading a complex content from the back-end subsystem generating web pages and sending them to the client device together with the event engine; - the event engine is configured for being loaded in a user's browser and, once playing of the user experience has commenced, for extracting events from the complex content and dynamically activating various multimedia components according to time cadences established by the author with the editing sub-system; - the event engine is adapted to activate web applications in the client device (105, 115) allowing user interaction.