The Ultimate Grammar Resources Guide on the Web for the SAT/ACT
An Ultimate List of Grammar Guides
The grandfather of all University guides on grammar is Purdue’s OWL. OWL stands for “Online Writing Lab” and has been around for years. I think I discovered OWL back in 2007 or 2008. A past co-worker who graduated from Purdue told me they had an incredible resource for students and she valued it so much. Since then, I’ve seen it referred to constantly. I’ve used it myself to aggregate exercises for many past classes. It’s a great place to start.