WikiPedia

https://www.wosign.com

https://www.startssl.com

https://letsencrypt.org/   https://imququ.com/post/letsencrypt-certificate.html

https://www.verisign.com/

https://www.geotrust.com/

https://sg.godaddy.com/zh/web-security/ssl-certificate

https://ssl.comodo.com

 

HTTPS Everywhere is a Firefox, Chrome, and Opera extension that encrypts your communications with many major websites, making your browsing more secure.

https://www.eff.org/Https-Everywhere