This Arduino-controlled open-source automated filter-wheel changer is set up to move to 8 different filter positions. Normally these devices are used in scientific experiments that need good optics. Commercial versions cost over $2,500 and you can make this yourself for less than $50. So if you make just one -- you more than justify the purchase of your own open source 3-D printer!
This component is part of the Open-source optics project, whose goal is to radically reduce the cost of scientific optical hardware: by the Michigan Tech's Open Sustainability Technology Research Group.
For similar see the Open-Source Lab How to Build Your Own Hardware and Reduce Research Costs
This project was featured in an article and podcase in Science. Pearce, Joshua M. 2012. Building Research Equipment with Free, Open-Source Hardware. Science 337 (6100): 1303-1304.