Enlightening Neat app, works well for basic optics design. Also doubles-up as a whacky etchasketch if you have enough imagination and patience.
2.0 - Redesigned and improved! We've listened and now the app is much easier to use - including drag and drop rearranging of elements. Comments welcome!
1.5.6 - Fixed a bug related to the "next waist" Gaussian optics calculations. Added more file information to the load/save interface and improved the UI.