Sockets
This library I wrote is very similar to the System.Net sockets class. I never built any code to host a socket, but others have taken it and added it to make things like a WP7 web server.
File System
This library is very similar to the System.IO classes to read a directory or a file via a file stream. The phone is pretty locked down, so the only place I’ve been able to read is the \Windows folder. There are several ways to get those files off the phone. One ingenious solution given to me by a good friend (not sure he wants to be named or not) is to base64 the file and view it in the text viewer in the debugger. The other way is to upload the file to a web server…or use the sockets library above.
Read more: Jer's Hacks