We use Disqus as our comment platform on the website and our new policy now requires that you create a Disqus account before commenting.
We use Discord as our subscriber & staff chat platform.
We use Vimeo (formerly VHX) to host our video archives in 2016 and beyond. Prior to that, we used Gumroad to provide video archives (2015 and earlier).
Ultiworld accounts are used for all other features on ultiworld.com, including buying and accessing an Ultiworld subscription.