Executing data in RAM, not on disk

I want a program to ``download'' an executable payload, but only keeping it in RAM, not writing to disk. Then I want it to execute what it just downloaded. So instead of saving it as a file and then executing it, I want the program to be able to execute what's running in RAM, possibly being stored as a string or something. Is this possible or am I just stupid?

The only thing I can think of would be a virtual RAM drive or in-memory database but that's way too complex and would make the downloader too big. I am looking for a more compact and portable solution.