CPU: RDC R3211 SoC (not much info about it on the manufacturer's site, http://www.rdc.com.tw)
WLAN: Ralink RT2661 in a mini-PCI slot (MIMO XR, http://www.ralinktech.com/prod-2661.htm)
Switch: IC IP175A, 4 LAN, 1 WAN port.
Seems like serial and JTAG is there.
Products also based on this SoC: Gemtek WRTR-137G and Edimax BR-6216Mg, these have 2Mb flash and 16M memory, so this board might also have these values, hard to determine by the pictures. Interesting thing on the FCC photos is the WRTR-136G on the bottom of page 5.
Did not checked yet if it runs Linux or if there is a GPL tarball, will do so soon.