re: Sharing schematics. I see what you were getting at, regarding building a system out of multiple boards designed using different EDA packages. The Good News is that you can get viewers for OrCAD, Altium Designer and PADS, so you don't need a license to install the full-up software just to view schematics or PCB artwork. The viewers are important, because the symbols on professional schematics include lots of metadata that are needed to actually build the board. There's a part number of some sort (either direct vendor part number or company-standard part number) used for the bill of materials, and of course a PCB footprint reference.
Interconnects between boards need to be defined fully and documented in some standard way.
What definitely doesn't happen is that Group A does a board in Altium Designer and passes the design files off to Group B who use OrCAD and want to import the design into that package. Such translations fail more often than not. There are library translation problems, database problems, all sorts of issues that make such translations problematic. If Group B really needs to work on the design in OrCAD, then need to make sure that their library has all of the symbols, all of the footprints, all of the other data to make it happen, and oftentimes it's easier to simply recapture the schematic in the other tool that to expect the translated schematic to generate a netlist that the translated PCB design won't choke on.
Anyways, my point is, I guess, that as long as the source files are available, as well as a viewer, then that's the best thing for schematic sharing when the friends' only need is to look at schematics and PCB artwork. If you need to actually modify the designs, you need the proper design software and probably the original library.