One of the things that makes it hard to produce a truly portable hybrid computer is the need for a traditional keyboard. You either have to fold the keyboard away somewhere, which adds awkward bulk; or instead detach it completely, which inevitably means when you need the keyboard the most, it's probably been left behind at home or at the office.

Lenovo is shrinking the hybrid idea down into something closer in size to a paperback book than a laptop. The new Yoga Book has a clamshell hinge and a 10.1-inch full-HD-resolution display, but where you'd expect to find the keyboard is instead a blank slate.

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In one mode, that acts as a Wacom-style drawing tablet, and works with the included Real Pen stylus. A few built-in Lenovo apps helps you take notes and annotate documents, and it should work with Photoshop and other visual art programs.

But, at the touch of an on-screen button, the drawing tablet is replaced with a backlit keyboard, which Lenovo calls the Halo Keyboard. It's akin to on-screen typing on an iPad, but the matte surface is much better for finger control than a shiny laptop or tablet screen. In a brief hands-on test, I found finger-typing on the Halo Keyboard to be very doable once you get used to the key size and placement, but in the pre-release version I tried, there was a little more lag than than I'd like when typing quickly.

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If this idea sounds familiar, and not in an iPad on-screen keyboard kind of way, then you're a real connoisseur of obscure computers. I reviewed an early version of this concept back 2011, when Acer released its 14-inch Iconia dual-screen laptop. In that case, the bottom of two touchscreens could display several on-screen keyboard layouts, other touch tools, or just extend the desktop onto both screens. The idea clearly didn't catch on with the public as there was never a version 2.0 of that Iconia, and this is the first no-physical-keyboard Windows clamshell I've seen since then.

And when you're not typing or drawing, the system can fold into a kiosk or tablet mode, just like any other laptop with the Yoga name -- it's just that this one is a lot smaller.

Powered by an Intel Atom x5 processor, the Yoga Book is available in both Windows 10 and Android versions, and weighs around 1.5 pounds (680 grams). It'll start at $499 and £449. Australian pricing is yet to be confirmed but the US price converts to around. AU$665. It should be available immediately.