I’ve created my first app for sale on the AutoCAD Exchange Apps Store. The app is a single command which extracts all of the boundaries from surfaces in a drawing. It’s a fairly light weight app that I use on occasion to combine into an overall surface boundary. The program is compatible with Civil 3D 2013.
I’m working on a more involved App used in River Sections which is almost complete. A video of what this future can do may be found here: http://civilintentions.blogspot.com/2012/09/river-sections-for-civil-3d.html