Beetle Bits or the Morton System. Beetle Bits is made in the USA and Ray (the inventor) is very helpful if you have questions. I personally have the Morton because I bought it before I knew about the Beetle Bits. Beetle Bits have different sized grids you can get that also work with some other nifty doodads like the Cuttersmate. Even with the grid you won't always get perfect squares, it depends on how the glass scores. You can also make diamonds with both cutting systems.

Thank you!