Confetti is a high-performance, easily-configurable particle system library that can animate any set of objects through space. You can specify your starting conditions and physical conditions (e.g. X and Y acceleration, boundaries, etc.), and let the confetti library take care of the rest.
Particle systems are often used in games for a wide range of purposes: Explosions, fire, smoke, etc. This effects can also be used on normal apps to add an element of "juiciness" or Playful Design.
Precisely because its main use is games, all engines have support for particle systems, but there is no such thing for standard Android UI.
This means that if you are building an Android app and you want a particle system, you have to include a graphics engine and use OpenGL -which is quite an overkill- or you have to implement it yourself.
Leonids is made to fill this gap, bringing particle sytems to developers that use the standard Android UI.