Add Super Productivity

[SedjamTan]

1. Super Productivity is under MIT License since 2018.
2. Source Code available
3. Privacy Policy indicates that apart from optional sync features they don't collect any info from users unless required by law.
4. Possibly no proprietary elements.
5. It is mostly stable.
6. Still in active development since at least 2017 or earlier. Android app possibly first released at Google Play at around 2020.
7. Has a wiki listed in their github page and has guides in their website.
8. Free of charge

[offa]

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