Marketcetera uses FIX, I am trying to get that working on my machine now, last time I tried I did not succeed but this time I have at least some parts of it working.

For end-user GUI it uses http://www.marketcetera.org/confluence/display/PN/Photon which is the part I am having a hard time with. Apparently it works out of the box on Windows but on Linux its ability to use more than one kind of browser's underlying libraries for rendering causes conflicts so the one they provide for Linux crashes and so far so has every one I have tried to compile for myself.

I am glad to hear that FIX does have some kind of signing, even if "braindead", as I was worried that real world financial institutions didn't seem to be concerned about ever being able to prove who ordered what...

-MarkM-