Ask HN: Membership hosting / CMS

Just got this question from a friend but I don't know about membership sites outside of WordPress. If you could give me some ideas, I'll pass them onto him. Thanks!

Q: In the future I'll need a membership website. Its to host my Squarespace templates. Paid users can login into the site, manage their account details, etc. Do you know any website hosting that offer this? I know Wordpress have several plugins, but I can't use Wordpress.