Remove ethercalc (unmaintained since 2020) (#3919)

README.md

@@ -1478,7 +1478,6 @@ An [office suite](https://en.wikipedia.org/wiki/List_of_office_suites) is a coll
 
 - [Collabora Online Development Edition](https://www.collaboraoffice.com/code) - Collabora Online Development Edition (CODE) is a powerful LibreOffice-based online office that supports all major document, spreadsheet and presentation file formats, which you can integrate in your own infrastructure. ([Source Code](https://cgit.freedesktop.org/libreoffice/online/)) `MPL-2.0` `C++`
 - [CryptPad](https://cryptpad.org) - CryptPad is a collaboration suite that is end-to-end-encrypted and open-source. It is built to enable collaboration, synchronizing changes to documents in real time. ([Source Code](https://github.com/cryptpad/cryptpad)) `AGPL-3.0` `Nodejs`
-- [EtherCalc](https://ethercalc.net/) - Web spreadsheet. ([Source Code](https://github.com/audreyt/ethercalc)) `CPAL-1.0/Artistic-2.0` `Nodejs`
 - [Etherpad](https://etherpad.org/) - Etherpad is a highly customizable Open Source online editor providing collaborative editing in really real-time. ([Demo](https://demo.sandstorm.io/appdemo/h37dm17aa89yrd8zuqpdn36p6zntumtv08fjpu8a8zrte7q1cn60), [Source Code](https://github.com/ether/etherpad-lite)) `Apache-2.0` `Nodejs`
 - [Grist](https://getgrist.com/) - Grist is a next-generation spreadsheet with relational structure, formula-based access control, and a portable, self-contained format. Alternative to Airtable. ([Demo](https://docs.getgrist.com), [Source Code](https://github.com/gristlabs/grist-core)) `Apache-2.0` `Nodejs/Python`
 - [Infinoted](https://github.com/gobby/gobby/wiki/Dedicated%20Server) - Server for [Gobby](https://github.com/gobby/gobby/wiki), a multi-platform collaborative text editor. ([Source Code](https://github.com/gobby/gobby)) `MIT` `C++`