3dSen PC is an NES emulator with a unique and very cool twist: It converts games, "both classic and modern homebrew," into full 3D in real time. Everything works as it normally does—game mechanics are unchanged—but camera angles and zoom can be adjusted on the fly, so if you wanted to play some isometric Super Mario, for instance, you can. It's been in development for about five years, and today it went live on Steam Early Access.
The emulator currently supports Steam input, the ability to create save states, and "dynamic skyboxes," and the Early Access FAQ indicates that a first-person view is in the works too, although that's still being worked out. The list of games it supports is "ever growing," too.
The Steam page says the trailer at geodstudio.net "doesn't do it justice," but a separate video by speedrunner Kosmic really does. You can see the "normal" 3D perspective in action, but he also shows off camera rotation during gameplay and some visual oddities that can result. It turns out that Mario looks a lot better from the side than he does head-on.
3dSen is not free, and I have to wonder whether the author selling the software on a prominent store might prompt a quick and harsh reaction from Nintendo, similar to the fate that befell that really good Super Mario 64 PC port. Emulators themselves are legal, but Nintendo could still threaten a takedown or pressure Valve not to allow 3dSen to be sold.
Nintendo has never been shy about dropping the hammer on people messing with its stuff, and has shut down multiple ROM sharing sites in the last two years (ironically, the version of Super Mario Bros. Nintendo sold on the Wii's Virtual Console may have been downloaded from the internet). The company is still clearly anti-emulation, though, as evidenced by a statement that has been on its corporate site for years:
"The introduction of emulators created to play illegally copied Nintendo software represents the greatest threat to date to the intellectual property rights of video game developers. As is the case with any business or industry, when its products become available for free, the revenue stream supporting that industry is threatened. Such emulators have the potential to significantly damage a worldwide entertainment software industry which generates over $15 billion annually, and tens of thousands of jobs," it says.
"Distribution of an emulator developed to play illegally copied Nintendo software hurts Nintendo's goodwill, the millions of dollars invested in research & development and marketing by Nintendo and its licensees. Substantial damages are caused to Nintendo and its licensees. It is irrelevant whether or not someone profits from the distribution of an emulator. The emulator promotes the play of illegal ROMs, NOT authentic games."
For now at least, the Early Access release of 3dSen on Steam is $9/£6.50/€7, which may go up when the emulator goes into full release, and a separate version for VR is $20/£15.50/€17, although there's a free demo available for that one. It's the first emulator on Steam that we know of, though emulator frontend RetroArch is also planning a Steam release this year.