It depends, you can do this with GBA emulators for example. For a lot of PC games probably not. However you might want to look at Nucleus Co-Op - that is capable of adding split screen functionality to PC 100's of PC games that don't officially support it. Another solution it to use one PC, run a couple of virtual machines. Pass a dedicated GPU though to each VM along with some usb ports, then connect a monitor to each dedicated GPU and a keyboard, mouse, or controller to the USB ports assigned to each virtual machine and have multiple people gaming one one PC like that. This PC would have to be setup specifically to do this using a hypervisor like Proxmox. A very extreme example of a setup like that here: