This portlet adds Disqus, G+ and Facebook as comment engine options. You can use then in addition to Liferay comments or you can replace it with one of them.
The portlet is implemented as OSGi module and works in Liferay 7 and DXP only. Check older branches for Liferay 6.1 and 6.2 compatible code.
To compile and deploy it simply run "blade deploy" it will deploy it to your local running instance.
See more information at http://javaguru.fi/projects/social-comments-portlet