What do most servers use for their portal websites such as http://arkhamnetwork.org the portal that shows Forums | Staff | Donate ETC. What web hosting company do they use for that? And what do most servers use for it?
That's only like a 20kb page, any host will do fine, but if you plan to run a forum like XenForo you may need to find a host with less limitations in the future.
You asked what they use. The answer is that it is probably a web server installed on one of their dedicated servers behind Cloudflare.
Arkham uses nginx (with PHP-fpm), likely on one of their dedicated servers or a seperate VPS. Desteria uses a similar combo.