When Valve announced its Index VR headset back in April in a bid for the best VR headset crown, it also shared screenshots of Aperture Hand Lab, a tech demo designed to showcase the capabilities of the Index controllers. The controllers are noteworthy because unlike those for other VR headsets, they track individual fingers rather than just clenched-fist hand movements. That tech demo is now available on Steam, if you want to try it for yourself, and you don't even need an Index to play it.
Aperture Hand Lab also runs on the HTC Vive headset, although aside from a bit of sightseeing that seems like it would be kind of a wasted effort, because the Vive doesn't support the Index controller. The main features, according to the Steam listing, are grabbing, shaking, and waving, all of it taking place within the confines of Aperture Science, the oddball setting for the Portal games.
If you don't have an Index headset (and you don't, because it's not actually released yet) or a Vive, you can still get a feel for what Aperture Hand Lab all about courtesy of Road to VR, which describes it as a "short game" that "passes you through several tests administered by a number of ‘personality cores’, the very same as seen in Valve’s landmark VR demo The Lab." Each core will give you a particular test to accomplish, but you can apparently freeform it if you like by throwing the horns, flipping the bird, or whatever else comes to mind, which will elicit different reactions.
Despite the Portal trappings, Aperture Hand Lab was actually developed by Cloudhead Games, which has been working with Valve on VR for a few years. It's free, which is a pretty big plus, especially since there's really not much to it; it is not, however, the "flagship" game mentioned in April. According to the Valve News Network video below, which is also embedded in the Aperture Hand Lab Steam page, that remains unannounced. VNN also said that while Valve is working on three big VR games (something that was first revealed in early 2017), only one of them—the flagship—will be out this year.