run program in dll mode (if that is the right concept)

[LMHmedchem]

I have a program that I would like to be able to call from other programs and pass data between the two programs though memory (meaning not file based). The program being called (calledApp.exe) is in cpp, and I would like the other end (callingApp.exe) to be flexible, meaning that there would be appropriate abstractions to allow callingApp.exe to be in cpp, java, browser based, etc. In short, I would like to make my program a tool that can be called by other programs at runtime, not an API to include at link time.

I think that one way to do this would be to have calledApp.exe be some kind of dll, but I don't really know enough about this to even think about the problem properly. Can some one point me to a good reference that would give me the basics for the possible ways things like this can work? Some sample code for simple programs would be great as well. The data would probably be passed between the apps using pipes or shared memory, but I know java has things like stream, etc, so that part of the code may be abstracted as well.

This also will need to run under windows xp, win7, linux, and OSX, so that is another consideration as well.

I know this is a very open ended question, so I appreciate you patience. I will be able to ask better questions once I get a bit further into this.

LMHmedchem