Intel's Atom SoC has enabled a new breed of tiny computers although one Chinese vendor has taken it to the extreme. Shenzhen Apec Electronics is now offering an Atom-powered PC that's roughly the size of a Chromecast dongle.
The APM-D01 measures 3.9" x 1.5" x 0.38" (100 x 38 x 9.6 mm) and tips the scales at just 1.6 oz (46 g). Systems are available with your choice of quad-core Atom Z3735F or Z3735G. Both 22-nanometer chips are clocked at 1.33GHz and can burst up to 1.83GHz - the difference is in maximum memory capacity and memory bandwidth.
Both tiny PCs include one HDMI output, one micro SD card slot, two micro USB 2.0 ports, 802.11n Wi-Fi and Bluetooth 4.0. Systems are available with your choice of 16GB or 32GB of internal storage. There's another port on the end of the PC stick which I assume is for the AC power adapter as no other I/O port is listed in the specs.
The system is capable of running Android, Windows 8.1 and Linux meaning might make for a decent HTPC or a light-duty desktop machine. That is, of course, if you're about to get your hands on one.
My only concern with a system this small is whether or not heat would be an issue.