Who could forget Google Glass? The experimental head-worn computer that promised to revolutionize technology. If only it a) had a purpose, b) had decent battery life c) didn't cause revulsion wherever it was worn. From privacy concerns surrounding Glass's built-in camera to the worry that the technology would erode human relations, hostility abounded.

Because Glass didn't have a single USP, Google was pretty much throwing an idea at the wall and seeing what stuck. And it turned out that very little did, so after a hardware revision, Glass made a muted exit from the public's consciousness.

At least, until earlier this year, when the company revealed it had placed Glass headsets at various business. Google Glass Enterprise Edition is designed to enable factory workers and other professionals to have a heads-up display while they work. Sure, it won't be as ubiquitous as the smartphone, but Glass can't be written off as a total failure.

Avegant Glyph (2016)

In the wake of Sony's exit from the market, other companies, like Vuzix, have tried to fill the void for personal-cinema fans. Perhaps the most eye catching is Avegant, whose Glyph headset looks like a pair of Beats headphones. But, flip the body down to eye level, and it instantly becomes a screen that claims to substitute a 55-foot movie theater. There's no indication how many headsets Avegant has sold; although the fact that its price has now fallen to $500 may be a sign of some success.

Royole Moon (2017)

Royole's Moon, the head-mounted display that inspired this jaunt through time, is the latest personal cinema to make its debut. The hardware comes with plenty of useful features, including a built-in browser, touchpad controls on the right ear cup and active noise cancellation.

Unfortunately, for all of those perks, the unit is still pretty heavy, and eyestrain remains an issue. Not to mention the whole fact that, like most of the devices on this list, it's pretty spendy. In fact, it's another $800 slab of plastic and leather that, like so many that preceded it, has to do a lot to convince users to open their wallets.

Daydream View (2016)