The Kyocera Echo debuted in 2011 with Android Gingerbread (2.3) -- that was even before Google started officially supporting Android tablets with version 3.0/Honeycomb. The two displays on the Sprint exclusive measured only 3.5-inch each; the phone didn't even support 4G networks. The Echo also had an unusual hinge design that that extended to the middle of the second screen instead of the more common book-like divide. Still, the chunky phone introduced many of the usage modes touted on future dual-screen phones, such as running separate apps on each screen or having an app span both screens, but only with supported apps.
The ZTE Axon M was announced to great fanfare in the US in what turned out to be a splash before the US government grew more averse to handsets by vendors of Chinese cellular infrastructure. Looking a bit like two iPhone 5s when extended, the Axon M hosts its screens are on the exterior of the device. It also supports multiple apps on each screen as well as mirroring an app on two screens for easier viewing by another person via a modes button located next to what has traditionally been Android's three main system button controls.
Not all Android dual-screen devices have been phones. The Sony Tablet P, released in 2012, was the Android-based keyboard-free answer to its wide-screened Vaio P laptop. The device had a curved exterior and could be used as a clamshell with the lower half sporting a software keyboard or gamepad interface for playing PlayStation classics.
Windows has also had its share of dual-screen clamshells. One of the smaller ones was 2010's Toshiba Libretto W105, which hosted two 7-inch displays. Released in honor of the company's 25th year in the PC business it has since spun out into a new company called Dynabook, the W105 sought to pick up the innovation mantel from the company's pioneering line that embodied mid-90s Japanese subnotebook cachet. Poor battery life and a lack of touch optimization were among the product's downsides.
Compared to the W105, the Iconia 6120 represented a more practical laptop form factor, with one of its 14-inch displays accommodating a keyboard closer to the size of a standard laptop size. This helped typing speed, although the device was still no match for a tactile keyboard. The second LCD also contributed to the thickness of the device.
Among Acer's supported gestures, tapping all 10 fingers on the lower deck cleverly called up the keyboard. Like the W105, though, limited battery life reduced the whole package's appeal. Acer went on to experiment with novel keyboard placements but has stuck to the tactile.
The Kno digital textbook was developed under a sensible premise. College textbooks are often spread flat and their content is often annotated, commented on and shared -- all great reasons for a digital display. While far more portable than a backpack of college textbooks, the Linux-based Kno, though, was large and heavy. It boasted two legal-sized screens side-by-side and supported digital sticky notes, highlighting, and annotation. You could even "freeze" a page on one screen and navigate to others for reference. Kno said it would offer tens of thousands of textbooks.
Alas, the pricey device never shipped. But its assets were picked up by Intel, which developed the Surface Neo's Littlefield processor with dual screens in mind.
The Surface Pro may now be the most recognizable 2-in-1, but the concept got rolling with the original Yoga convertible. When rotated into tablet mode, though, these devices are thick compared to pure slates such as the iPad, so Lenovo has experimented with reducing the thickness of the keyboard in the Yoga Book line.
The second generation introduced a second E-Ink display for hosting a keyboard and which can also be used for annotating PDFs and other tasks (but which can't display the full Windows interface). Lenovo is still interested in such displays. It is an investor in CLEARink, an E-ink competitor for low-power reflective displays.
Whether you consider the LG G8X ThinQ a dual-screen device comes down to semantics. Officially, the second screen is an accessory that mates with the device using a case, but carriers are essentially bundling the case in as there's little reason to get it otherwise. The case an optional second screen has its merits as it doesn't weigh you down with extra bulk when you're using it alone.
The G8X represents a big improvement over LG's previous attempt in the space, the V50's accessory screen, as the G8X second display matches the size and shape of the phone's screen down to the camera cut-out notch.
Positioned as a blend of the best of Microsoft and Google, the Android-based Surface Duo marks Microsoft's return to the smartphone space, and it is the smaller cousin of the Windows-based Surface Neo tablet. It supports Google Play, but Microsoft will have a suite of its own apps resident on the device and is aiming to make gestures consistent with other dual-screen devices that run the forthcoming Windows 10 X. It's expected to ship in late 2020.
Like the second display accessory for the LG G8X, the CastAway will pair with a range of supported smartphones with an accessory case. But unlike that device's second screen, the CastAway may be the world's smallest ChromiumOS tablet. Available in 5.8-inch and 6.3-inch screen sizes, the device runs a routine to check certain folders for new media to display. You can tear away its 360-degree magnetic hinge to show photos to a friend.
It also has a few other tricks up its sleeves, such as two USB-C connectors that enable it to serve as a portable charger or to work with accessories such as a keyboard or mouse. A long press of its power button will quickly boot it up as a glass Bluetooth keyboard. It's expected to ship toward the end of spring 2020 after its Indiegogo campaign.