I've used Kiwi syslog server in the past before it got purchased by Solar Winds. I think that it is still free at
http://www.solarwinds.com/register/registration.aspx?program=874&c=70150000000EIV7 It wored great but I finally wrote my own software to receive and store UDP syslog messages to a sqlite database.
I've been running Monowall for years on a tiny compact flash drive and $100 embedded hardware from pcengines.ch. It is easy to configure and runs on just a few watts.
Alternatively, you can get a cheap embedded system and run a syslog server on it. I can do that on my DLINK NAS drive or get something small like an Ethernet Arduino running off a USB or Power over Ethernet connection. The Ethernet Arduinos include an SDcard slot.
http://www.arduino.cc/en/Main/ArduinoBoardEthernet