This is a theme component that will allow you to easily add extra social providers to the share button on posts.
Some providers & Links:
English Social Media
https://www.stumbleupon.com/submit?url=[/s] Replaced with mix.com
https://www.instapaper.com/edit?url= (currently European users can not access because of the GDPR)
Non-English Social Media
Phone/Audio-Based Social Media
https://web.whatsapp.com/send?text= (read also https://meta.discourse.org/t/social-share-component-with-whatsapp-web/108684/11?u=dax)
This guide is a wiki, if you have other providers, maybe specific for your country, just add them to the list.
You will find the share URL in the documentation for the developers.