Russian Math Workbooks
One of the achievements of the Soviet Union was that they took math and math education very seriously, and they developed a well-deserved reputation as having some of the best mathematicians in the world. What is usually presented as "Russian Math" in the U.S. is not the famous program that produced so many great mathematicians but rather a program that has been watered down over the last 20 years by other math traditions, modified to be more like different U.S./UK-based curriculums.