PreAlgebra
Grade 7 in full plus most of Grade 8, ending ready for Algebra 1.
1,565 interactive problems, free to use.
An accelerated middle-school course covering Grade 7 in full and most of Grade 8, so students finish ready for Algebra 1.
It works through signed numbers, proportional reasoning, and percent before introducing equations. Every problem is interactive, with a hint and a worked solution.