When is an all-in-one desktop not an all-in-one desktop? When it's one of the newish breed of portable big-screen computers we call tabletop PCs. That's essentially either an all-in-one PC with a battery in it, or a giant lap-size tablet, depending on your point of view.
Acer is joining HP, Lenovo, Sony, and others in releasing one of these hybrid systems with the just-announced Aspire Z3-600. While most of the other tabletops we've seen have 20-inch screens, the Z3 has a 21.5-inch display (only the 27-inch Lenovo Horizon 27 goes much larger), and a folding hinge to either keep it upright, or else lie down flat on a table or desk (in practical experience, these often end up on ottomans, where a lot of two-player air hockey is played).
At under $800, that sounds like a good deal for a tabletop PC, especially for one with a full-HD display, Harman Kardon speakers, and an HDMI input for using the display with a game console, Blu-ray player, or other external source. The catch is twofold: the battery is only rated for 2.5 hours (but realistically, most tabletop PCs aren't meant for long-term battery use); and the CPU isn't even a low-end Core i3, it's an Intel Pentium processor. The included 4GB of RAM and 750GB HDD are standard enough, no complaints there.
The Acer Aspire Z3-600 will be available later in December for $779.