Listserv with community & CMS baked in. Feels dated.
I used this platform as a contractor for a client in 2015. I've completed the organization demographics on behalf of the client I served.
The good: This is a big, big, big product. Lots of features, including a fully-functional membership management system for organizations who need to do more than just engage their users (e.g. track event attendance, membership dues, volunteering, etc.). This product is very listserv-esque. As a member, you never have to visit the community if you don't want to. You could fully engage in a Socious community by email. The CMS is fully-functional for most organizations, and it could easily serve as both your public-facing website and community. The customer service is excellent. Any big issues get attention from one of the owners.
The bad: The administrative area is a bit complicated at first, but I got the hang of it quickly after reading help documentation and attending some extra training. Despite getting a design refresh recently, the product still feels a bit dated, but that's overcome with some CSS work, which Socious is willing to do for a fee.
Bottom line: I'd recommend this product to any organization that has an experienced community manager with good technical skills -- especially if the users are more likely to engage by email than online.