Transmission

On the openmss forum you can find image to install. Someone there made an image from the Central Axis "firmware" that enables ssh etc. After you have done that you can install Transmission daemon from the optware feed with the ipkg command. You can ask for help on the openmss forum.

Without researching what's new out there since last summer I suggest Bubba|TWO server.
You can use it as server, router, wlan ap, nas ...

http://excito.com