Skini is a platform for composing and producing live performances with the audience participating using connected devices (smartphones, tablets, PC, etc.). The music composer creates beforehand musical elements such as melodic patterns , sound patterns, instruments, group of instruments, and a dynamic score that governs the way these basic elements behave according to events produced by the audience. The platform allows to control the musical quality of the work, even if during the concert or the performance, the audience interacts with the system giving birth to an original music creation. Skini scores are expressed in terms of constraints on events that control which musical elements are accessible to the audience and when they are available. Constraints may be instantaneous , for instance one constraint may disable violins while trumpets are playing. They may also be temporal, for instance, one constraint may prevent the piano to play more than 30 consecutive seconds. The Skini platform is implemented in Hop.js [10], for the general infrastructure and most of the user interfaces, and in HipHop.js [13], a reactive synchronous DSL, for implementing the music scores. The HipHop.js constructs, which consist of temporal operators such as parallel executions, sequences, awaits, synchronization points, and preemption, form the core implementation language for expressing Skini musical constraints. This paper presents the Skini platform and It reports about live performances and an educational project. Some musical pieces created with Skini can be found at: https://soundcloud.com/user-651713160