I had never seen or heard of an open-source program for viewing LIDAR data, which is increasingly in use. I do not use LIDAR in my daily work, so it seemed like an interesting challenge. I hoped to find something simple to be able to load an occasional LIDAR data set for exploring.
There are several extensions and add-ons out there. After searching, I found FUSION software by the Pacific Northwest Research Station / Forest Service. It is stand-alone software. A new version was just released in early February 2012. Recent and continual updates for any open-source software are always encouraging to see and to maintain its relevance. The website includes sample data (for Washington State below) and a well-written manual.
The screenshots show the wide range of graphics that FUSION can produce. After importing an aerial image/DOQ and the LIDAR data, you select an area of interest, and a new window automatically opens. One can perform a variety of tasks simply by right-clicking--including generating a canopy surface model and even producing anaglyphs for 3D. There is even the very appropriately named "Wiggle-Vison."