Latest stable release
Sketchyphysics RC 1 (More here)
Sketchyphysics 3 Experimental
More advanced scripting, with collision events and triggers, and limited sound effects are all confirmed for this experimental version. SP3 X is effectively a testing ground for ideas and control systems that may or may not be included, in some form, in SPIV.
On touch (on collision) and on tick (on trigger) will be added to the UI for any physics body. On touch allows you to perform actions like playing a sound effect, or changing a global variable, whenever any collision between the selected object and another other part of the simulation occurs. The use of sound is limited due to SketchUp's play_sound command; only one sound can play at a time, and it can't be altered. This means that conventional physics sound effects, like a rock falling on the floor, won't work properly; true sound support may be added in SPIV.
Upon release, it should be noted that models made using it will most likely not work with future versions, including SPIV.