There are mods, and then there are projects that go so far beyond mods that they might as well be their own games. That's the case with Skyblivion which, if you couldn't tell by the name, is a recreation of Oblivion using the Skyrim engine on PC.
One group of dedicated developers decided that they really wanted to revisit Oblivion within the Skyrim engine and, since Bethesda appears to be in no hurry to give the game a major facelift, they took it upon themselves to do exactly that.
If you watch the above video, you wouldn't be faulted for thinking, "well that's certainly a nice-looking RPG world, but what's the big deal?" What you need to take into account is that this is a fan-created mod within the PC version of Skyrim that includes a completely rebuilt version of Oblivion inside of it. If you go back and watch some videos of Oblivion in action, we feel pretty confident you'll understand what makes this project so special. The whole freaking game world has been lovingly recreated from scratch.
As noted on the project's official website, this is a volunteer-based undertaking by the TESRenewal modding group. In other words, nobody is making a penny off of it, which is probably why the folks at Bethesda have been happy to let the project continue its course. It's also noted that this is a work in progress, so, while the video certainly makes it look like the mod/game is complete, there's still plenty of work to be done. The team is currently rebuilding Cyrodiil, which requires recreating all of its quests, locations and characters using tools from Skyrim. In other words, they aren't just rebuilding the lands of Oblivion using a new engine, the goal is to have a complete, functioning version of the game running in Skyrim when all is said and done.
For folks looking to play the project as it involves, the Skyblivion mod is available to all. However, since the team is doing their best to keep things on the up and up as far as licenses and whatnot are concerned, the mod won't actually work unless you already own both Oblivion and Skyrim, as well as all of their respective DLC. That won't set you back much nowadays but, again, it's good to see they've gone the extra step to keep the project legitimate.
Our only question is, when will this project come to a grinding halt due to everyone involved being hired by various developers?