There is not really an operating system on NETMF boards.
All you have is a small ‘clone’ of the dot net frame work, including some classes for hardware access.
You should look at the NETMF SDK API docs and the GHI API docs.
And I don’t think that ram or CPU power is the reason for only one Networking device. Specially the Raptor has plenty of both.
I think the main reason is that at the beginning nobody thought about having two network interfaces, so its not that easy to add a 2nd one, without breaking the first one or making it instable.
It just would take time to implement it for GHI, and since there a small company, that does not only NETMF stuff, and a lot of people waiting for other features (PPP, Application protection, …) it’s just not implemented yet.
By this, mIP or a device with it’s own stack and UART or SPI interface is the way to go I think.
And for samples, I think in the CodeShare section are some mIP sampels.