Free Math allows collecting digital assignments from students and enables quick grading by grouping similar student work on each question. You can assign problems for any existing materials and all of the work done by students is completely freeform, so it works for a broad range of classes.
Statistical Data Analysis -> Online and Easy
Funexpected Math is a beautiful interactive application for kids aged 3-7 featuring a growing collection of math-related games that teach various types of thinking and improve learning skills. Desktop version is free due to the Covid-2019 Pandemia
Mathchops helps kids build crucial math skills through AI-curated games. Versions for the SAT, ACT, and grades 4 - 11.