BioWare's Infinity Engine is the greatest RPG engine ever created. There, I said it. Sure, it doesn't support true turn-based combat, but when you look at the entire package - the way it handles dialogue to paper doll management to party-based adventuring to rules systems to gorgeous 2D painted backdrops - there isn't another engine out there that ticks off as many role-playing boxes as the Infinity Engine does.
And that's why I'm excited to report that someone has created an open-source and cross-platform implementation of the Infinity Engine called GemRB. At its current stage of development, the engine can be used to play through the entire Baldur's Gate saga, all of Icewind Dale, and some of Icewind Dale II and Planescape: Torment on everything from Linux to the iPad to smartphones, as seen on these YouTube videos. But let's not let the real promise be obfuscated by yet another play-through of those classics - GemRB can be used to build an entirely new Infinity Engine-based game:
While it would be great to focus development on one game at a time, ideas often occur for other games that are just too good to let go. This section is for those ideas, so that they can be recorded and not lost. If you're submitting a completely new idea, it might be good to see if your idea can eventually be incorporated with an existing project in some way, in effect bringing to bear the best traits of both. If you're going to hassle about licensing issues, please license your content under the GPL 2 to allow the greatest utility to the GemRB project… If indeed, you want GemRB to use it.Someone, somewhere, please take this and run with it before EA realizes the implications it might have. I will be indebted to you and will buy multiple copies of your game. Thank you.
New game development should be modeled off the game template, this gives you an outline and a couple questions directing you where to start creating an entire world, it's inhabitants, and major events. Other, more realistically ambitious templates include: Plots, Characters, Locations, Items, and Capabilities.
If you're filling out a template, you should fill out the sections relating to the idea you're adding and then provide appropriate links to the ideas in the other sections (if you're making a character, fill out the character information, but just provide a link and short description to the town the character lives in - fill out the town's information on the town's own page).