Asus launched the world smallest router last week measuring 6.5cm long and weighing 17.5g, the Asus WL-330NUL. It is available since 20th May 2013 for S$59.
The Asus WL-330NUL is a 4-in-1 router, it acts like a router, USB Ethernet adapter, Wireless adapter, and supports hot spot sharing!