hey hey

apart from two amps is there a amp or some software where two guitarists can play off the one amp or through one computer?
Can't really speak to the software. You mean like on one computer? Even if you could wouldn't that sound like shat?

If your (an) amp has two or more insert jacks you could run two guitars into it but again it would sound like shat, unless you two took turns playing. That would work.

Are you asking this for live playing or instruction/lessons purpose?