If it's different patterns like scalloped rectangles and so on, then it is most likely the Nestabilities diecuts from Spellbinders. Here's a link for you -
http://spellbinderspaperarts.com/nestabilities.
They will work in all the manual die-cutting machines with the right adaptor plates. And they are great, yes.
But for plain rectangles, a ruler with a steel edge and a sharp knife is how I do it. Tim Holz and Judikins both make clear rulers which have markings along them so you can see how much you are cutting, and a steel edge so that you don't accidentally cut the ruler!!
You can also buy punches - I have loads of circle punches. But once they get over a certain size, they are both expensive to buy and bulky to store, so in the long run the Nestabilities work out as good value.