Here you can download the lastest SmoothStep2D build. There are two available versions, the first one uses standard HTML5 Context 2D renderer to draw all scene elements, the second one uses WebGL context, check the documentation to see the differences between both versions.
SS2D Context 2D: http://galloman.github.io/ss2d/lib/ss2dLib.js
SS2D Context 2D Minified: http://galloman.github.io/ss2d/lib/ss2dLib-min.js
SS2D WebGL: http://galloman.github.io/ss2d/lib/ss2dLibWGL.js
SS2D WebGL Minified: http://galloman.github.io/ss2d/lib/ss2dLibWGL-min.js
You can also download the entire project from githup repository if you want tu build your own version or build your game and all ss2d needed classes in a single minified file with Google Closure advanced compiler feature. It is also required to build realtime multiplayer client/server games with node.js and WebSockets.
SS2D Githup repository: http://github.com/Galloman/ss2d