Crystal Space
It is sometimes said that the best things in life are free, this holds true for Crystal Space. Unlike Genesis 3D this is a genuine open source project, licensed under the LGPL, a variant of the GPL for libraries. And as a 3D engine, this one is top notch, cream of the crop. It supports nearly anything a 3D engine can support, with the single exception of skeletal animation, but Quake 3 does not have this either. And it even has a built-in isometric engine.
Crystal Space is a free (LGPL) and portable 3D Game Development Kit written in C++. It supports: true six degree's of freedom, colored lighting, mipmapping, portals, mirrors, alpha transparency, reflective surfaces, 3D sprites (frame based or with skeletal animation), procedural textures, radiosity, particle systems, halos, volumetric fog, scripting (using Python or other languages), 8-bit, 16-bit, and 32-bit display support, Direct3D, OpenGL, Glide, and software renderer, font support, hierarchical transformations, …
Crystal Space currently runs on GNU/Linux, general Unix, Windows, Windows NT, OS/2, BeOS, NextStep, OpenStep, MacOS/X Server, DOS, and Macintosh. It can optionally use OpenGL (Windows, GNU/Linux, Mac, OS/2, BeOS), Direct3D (Windows), Glide (GNU/Linux), GGI (GNU/Linux), Allegro (GNU/Linux, DOS), X11 (Unix or GNU/Linux) and SVGALIB (GNU/Linux). It can also optionally use assembler routines using NASM and MMX.
You can use Crystal Space to develop a commercial, closed source game, as long as you do not change the CS code or simply keep your game code separated from it. You will, however, hardly be able to do anything useful with Crystal Space unless you have solid programming knowledge.
This project aims to provide a framework for Crystal Space developers to create interchangeable plugins and reusable code for use in games and other projects which can make use of such a framework.
This Crystal Space Tutorial represents an effort by the CS community to make the engine's learning curve a bit less steep. Anyone can contribute, and individuals who feel that they have legitimate topics to add to the list are encouraged to make suggestions for future additions to the tutorial.
There are already lots of projects using the Crystal Space engine, not even all of them games. And to my astonishment and delight, the RPGs seem to outnumber the shooter games. They are all linked from the CS homepager, I'll just provide links to a few RPG projects (they all seem to be 3D though, no project yet to use the isometric engine):
The objective of the PlaneShift Team is to create a virtual fantasy world in which a player can start as a peasant in search of fame and become an hero. We will focus our efforts in the reproduction of a real world with politics, economy, many non-player-characters controlled by the server that will bring to life our world even without players connected!
Bonez Adventures is a game which consists of several "minor" games (with a playtime of about 12 hours), where each one of them counts for an independent volume. These volumes are supposed to come out in couple of months each after the other. All of them have unique story with different locations, NPC characters, foes and weapons. They are altogether connected within greater complex story. Inseparable parts of the game are action intermezzos/ subgames, which are always composed in a way to fit into the story. Each of these intermezzos/ subgames may be played separately from the rest of the game and allow player to publish his high scores on the internet. Concerning Bonez Adventures style, it is 3D Roleplaying / Adventure game from a 3rd person's view. The game takes place in different locations, which offers classical adventure tasks as are: using some things on / in combination with the others, talking with NPC game characters, or solving logical problems. Player may find here number of hidden bonuses, which allows him to raise his character's abilities. Then there are action locations filled with traps and enemies.
