Ancient Beast is a FOSS game project that has been in development by Freezing Moon for a couple of years, tantalizing everyone with top notch concept art and 3D models.
After a rather large restructuring in game scope, where they changed from attempting to create a 3D RTS in the Blender Game Engine, to a 2D hexagonal TBS built on HTML5, they have delivered a promising gameplay prototype that offers a mix of Heroes of Might and Magic and Magic: The Gathering's gameplay.
Gameplay currently revolves around summoning creatures and using their abilities to defeat other summoners
Still in heavy development, the game still needs to implement the entirety of its sizable bestiary, as well as adding animated creatures by utilizing the models they have created.
So, if you have any skills in web development, jump aboard and help them complete this awesome game!
Now, on the opposite side of the adver-spectrum, I present AncientBeast, a Norse-mythology inspired multiplayer strategy game with roleplaying elements that has been in development for quite a while.
It has a huge web presence, with a Facebook group, Twitter account (hiss use identi.ca), Miro video group (nice!), DeviantArt group with tonnes of awesome art... We'll have to see what license they fall under in the end, the team are still pondering how they'll make an open game that can sponsor a couple of beers for the devs.
See those circles? They show progress of the individual aspects of unit development
Their development methodology is rather interesting as well, from the use of a shared Dropbox account to collaborate and share art, to the rather excellent Bestiary system they've developed to introduce players to the different units in the game, their stats and abilities, and show the development progress of the indicated unit. That's some AAA level stuff there guys.
One of many timelapses and tutorials
Another remarkable thing about their development process is how well documented their art production is... They have loads of timelapses and tutorials of the team's artists creating concepts and models, I can almost confidently state that it's the biggest repository of its kind in open gaming.
One thing to keep in mind though is that coding wise they've only broken the ice. They've started implementing the game using the Blender Game Engine, but in the 2 years since the original designs were written up the most awesome art has been produced and the programming side of things have stayed relatively silent until recently; something not many other FOSS games can attest to. So if you know Python/BGE, this would be a very good time to jump in and help out.
If this post has interested you, be sure to drop in on their IRC channel, they have both a webchat page and a tutorial to get a desktop IRC client running