Stealth is a leading provider of high-performance computer systems and peripherals. They have recently released their newest model - LPC-681 - a mini PC that can be held easily in your hands. It measures 6.54"(W) x 6.18"(D) x 1.89"(H) (166 x 157.5 x 48 mm) to be exact and comes with amazing hardware specs.
Equipped with Intel Core i7 4800MQ (Haswell) mobile processor, 120GB SSD (upgrade-able to 240GB, 480GB, and even 1TB SSD), 4GB of DDR3L RAM (which can be upgraded to up to 16GB), 4K resolution support, Ultra HD support, Triple Display support, built-in USB 3.0, Gigabit LAN, Serial DB9/RS232, e-SATA, Video (DisplayPort, 2x HDMI), Audio, optional 802.11 b/g/n wireless, and much more.
LPC-861 comes with Windows 7 Professional 32-bit or 64-bit and is Windows 8.1 compatible. It is a bit expensive considering the amazing specs. It starts from $2,395 and can go up with each upgrade. For example, $195 increase for 4GB of extra DDR3 SO-DIMM RAM, 1TB SATA 2.5 upgrade will cost you $275 more, etc. You can find the pricing for the system here.