Envisage have had a great deal of success with a number of free apps for Inventor. These can be found on the Autodesk Exchange App Store.
Here is a short description of these apps, their location & associated youtube videos.
3DPIPE - Create pipe runs from tabulated data (Video)
STLIMPORT - Import STL files into Inventor (Video)
IVIEWS - Auto-scaling drwing viewports (Video)
There are more apps to come from Envisage. Bookmark this Blog for future news.