How thick?
If similar to a welcome mat or rubber car mat, then a utility knife and a metal straight edge.
If in the 1/2" th hard mat and above category, you get into band saw, jig saw, dual blade saw or mini circular saw territory for me.
Again, guided with a metal straight edge or fence or a clamped straight temp wood guide.
If ur really good you can do a grease pencil line or chalk snap line as a cut guide and free-hand the cut.
Thicker the mat'l, the bigger tool ya gotta go to. But you knew that.
