Ayam is a free 3D modelling environment for the RenderMan interface. It features good RIB export, CSG (all RenderMan primitives supported), and NURBS modelling. Features instancing, arbitrary number of modeling views, object clipboard, independent property clipboard, n-level undo, console, and Tree-View with Drag-and-Drop support.
s3d is an XML schema for 3d scenes, objects, and so forth (intended primarily but not exclusively for computer games). The problem is that often as a games developer you need to work with many 3d editing tools and rendering engines, and there should be an easy and portable way to move objects, levels, etc. around. By having a common intermediate file format, you only need to write one exporter per tool and one importer per graphics engine. Also, you can develop generic tools which are not tied to any particular engine.
Grlib is an implementation of generative grammars and turtle graphics. The grammars (Lindenmayer systems) are used to produce descriptions of three dimensional objects, and the turtle is used to display them (i.e., generate images in several forms, such as bitmap, PostScript, or OpenGL).
XiStrat (aka 'Extended Strategy') is in particular about turn-based, networked multiplayer, non-cooperative, zero-sum, abstract strategy board games (e.g., Chess, Go, Reversi variants, etc.) on 3D-visualized polyhedra and contains a server, client GUI, autoplayer engine, utilities, and documentation. Related recreational modern mathematics (single agent, cellular automata, graph/group/complexity/knot theory, discrete geometry, algebra, combinatorics, and mathematical physics) is also dealt with.
KaGez-Production aims to make game developing under Linux easier. Tutorials and examples, reaching from simple console applications (non- graphical) to OpenGL games, are available, as well as tools like Image-Viewers, and 3D-Model viewers. All applications will be made for Linux only, most graphical items will work with GTK+/GNOME.
mjbWorld is a standards based 3D editor, which can graphically edit and allow users to see and interact with X3D (VRML) and other 3D formats. It is also intended to provide a platform which can be used to experiment with physics, animation, etc. Versions for Java, C++ and C# are included.