Free Math Sheets is a tool to generate math worksheet PDFs (and the answer keys if required). Currently it supports K-5 but I want to expand it to higher levels of math (Calculus, Physics, you name it!). You select a bunch of different options and then generate it. All in the front-end. No back-end or login in required. https://www.freemathsheets.com
If you are interested in helping out or forking it, here is the github repo github.com/sophikos/free-math-sheets
The paid project is Numerikos. I am going for something in between Khan Academy and Math Academy. I like the playfulness and answer input methods from Khan Academy (but it is linear, doesn't have a good way to go back and practice, etc.). I like Math Academy's algorithm (but it has multiple choice answers, yuck! and is easy to get stuck and doesn't have a good way to explore on your own). Currently Numerikos supports 4th and 5th grade math lessons and practice. The algorithm is based on mastery learning like Numerikos, but you can also see a list of all the skills and practice whatever you want. I am also working on a dashboard system where you can build your own daily/weekly practices for the skills you care about. Next up is 6th grade math and placement tests.