fstl is a viewer for .stl files.
Here's a screenshot:
(credit to Pranav Panchal)
It is designed to quickly load and render very high-polygon models; showing 2 million triangles at 60+ FPS on a mid-range laptop.
For more details, see the project page.
Issues and pull requests are welcome; the project is under 1K lines of code and should be fairly approachable.
(c) 2014 Matt Keeter
This work may be reproduced, modified, distributed, performed, and displayed for any purpose. Copyright is retained and must be preserved. The work is provided as is; no warranty is provided, and users accept all liability.
p.s. In my day job, I'm an engineer at Formlabs.
If you think fstl is cool, you should check out our
jobs page -- we're hiring software developers
and engineers of all stripes to work on interesting, hard problems in
consumer-level 3D printing.