Bentley Systems has an iWare Apps for Interoperability website where they've posted FREE apps for AECO professionals, including the following Revit plugins:
i-model plug-in for Revit
Publish i-models from AutoDesk Revit for open infrastructure information exchange with Bentley applications like Bentley Architecture and Bentley Navigator (a low-cost alternative to Navisworks)
ISM Revit plug-in
Coordinate, change, and synchronize structural data
RAM Structural System - Revit Link
Achieve interoperability between RAM Structural System (RSS) and Revit Structure
See the iWare Apps for Interoperability website for downloads, and for other non-Revit apps.