Add Free Math

[jaltekruse]

https://freemathapp.org

**This is a free and open source site that helps math students and teachers communicate more effectively. Students can easily record their full solutions to math problems digitally and save an assignment as a file that is submitted to their teacher through one of many learning managements systems (LMSes). Teachers take a zip file full of these students docs that they download from their LMS and load it into the site to quickly grade the whole class together, with similar work shown in groups. Both the student and teacher experiences work without logging in. **

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• I have read the Contribution guidelines and I am confident that my PR is suitable.
• This pull request has a descriptive title. For example, Add [App name], not Update readme.md or Added new entries.
• The app I added is not a duplicate.