bbPress
Default forum from WordPress.org is also tested and is found to be compliant.
Fully widgetized sidebars, header area and footer for easy custom widget and custom content the way you want to use...
Use of 580+ social icons enable you to add the icons the way you need them. Since they are font...
Tested for faster speed on Google page speed and gtmetrix and pingdom tools as well as made SEO friendly compliant.