Phlipple is a unique puzzle game. The goal of every level is to reduce a 3D shape to a single square. Elimination of squares is done by flipping edges around just like in a cardboard box. It starts off relatively easy to teach the basics, and provides hours of brain tickling fun. It's a great way to train memory as well as orientation in 3D.
sbs_proc (Side by Side Processor) is a simple command-line application that processes side by side stereo images (such as those produced by some mobile phones) and converts them into monoscopic versions which can be visualised on non-stereo systems. It works on .jps files and produces .jpg outputs. It can produce anaglyph (red/blue glasses required) or right or left images.
A lot of stereoscopic cameras use the .MPO format to store two JPEG images, including the Fuji W1, W3, and a few 3D camcorders that have a still mode. It can do two things for you: it can separate out the image files into a left and right pair, so you can process them or do whatever you want with them, or it can create an anaglyphic image (the ones you need coloured glasses to view). It is simple to use from the command line and takes wildcards, so you could process a whole batch of files with: mungempo *.MPO.
Cube Trains is a puzzle game where you build elevated railways in a city. It features 3D puzzles, unlimited undo/redo, and smart placement of pieces. The non-linear level graph means you don't have to beat a level before unlocking the next one. The game comes with a built-in level editor, so you can build and share your own corners of the city.
RoseThorn is a cross-platform library for 2D and 3D games running on GNU/Linux (and possibly other Unix-like OSes) and Windows. Features include: hardware accelerated 2D and 3D rendering; Ogg and WAV Sound support with OpenAL; Lua scripting; BMP, JPEG, and PNG image loading and saving (from screenshots); easily created and modified user interfaces with XML and CSS, combined with Lua event handling; separate 2D and 3D libraries; support for multiple fonts in both TTF and bitmap formats; support for OBJ, 3DS, MD5, and RTM model formats; skeletal animation (a work in progress); support for UDP and TCP networking; thread and mutex support; a Simple Shader API; 2D animated sprites; and some basic cryptography support. There is simple event management, with key/mouse bindings easily customized from the in-game console, config file, command line, or GUI.
Castle Game Engine is a cross-platform 3D game engine written in Object Pascal. It includes a flexible system of 3D objects, with out-of-the-box levels, items, intelligent creatures, and more. Rendering and processing of 3D models in X3D, VRML, Collada, and other formats is implemented. Many graphic effects are available, including shadows, bump mapping, shaders, mirrors, and screen effects.