Well not necessarily, you could code your own framework from the ground up ( X| ). Jk, find a system that you feel comfortable with and work with it. Google's framework and Microsoft's Azure platform are good starts. I think the latest Linux based cloud frameworks are still immature for commercial use. Actually, in all honesty, if you take away the bells and whistles you could build your own framework. The abstraction of the propagation of resources between platforms into a "cloud" is easy enough to code. I'd recommend sticking with a tried and tested system for business and work related development, but the aforementioned could be a fun code project.

Either use MFC wrapper classes or Windows API (try sockets, unless you want to write a totally custom driver). Use the Linux API sets for programs that you want to run on Linux. Alternatively you could use a third party networking solution (library), but I recommend coding a front end networking class that will load up different definition files based on the values of a set of macros (ex. #define OS WINDOWS). If your object oriented skills are up to par, then it should be no problem to write it once and port it to future programs, occasionally modifying the definitions based on the API updates/changes for each respective operating system you want to support.