I'm not certain as to which subforum this applies to, therefore I decided to post here.

So the gist of my problem is: Assuming I have access to a few college grade computers networked via LAN, and I can run code on all of them, what programming construct could I use to harness their combined computing power?
I don't have any particular program in mind, but for arguments sake, hash cracking, Blender rendering, Web scraping, probably data analysis? Are somethings that I can probably do with it. I need a client on the clients that can merely run one method that I provide and return the results. Think of this as the exact opposite of Java RMI, the client generally runs code on the server, but I wish a server can force a client to compute something and return the result. Perhaps even a single method. And one other feature is the ability to change that method on the fly without me needing to manually reinstall the client on every system.

Does anyone have any idea if something like this already exists? I'm thinking Hadoop doesn't have anything to do with this, but I might probably be wrong.

Any insight on what I could potentially use would be helpful, even if something like this hasn't been done, I'll develop it myself, I'm an amateur programmer and would love to learn to.