Does anyone have an easy free program for designing PCR primers?

I'm making DNA primers for PCR, and it seems like there has got to be a simple program to design the reverse primer. I have no experience in programming, but it seems like a program that reverses the order of bases you enter in and converts it to complementary bases would be quite simple to make. I'm trying to make it in excel, but I'm no excel expert, so hopefully people have already figured such a program out.