The SAP Community is ‘tabbed’.
Which means the entire community is hosted on the same website but hidden behind a tab. If you click on the tab, the community appears. But the rest of the navigation options remain the same.
This means the community has to maintain the look and the feel of the rest of the site, but 9 out of 10 navigation options take people away from the community. To navigate around, members must hover over the tab and select where they want to go.
The upside of this is it likely helps with search engine rankings. The downside is it makes it really difficult for members to discover everything the community offers. That navigation bar really does matter.
The Alteryx community is a bit different. The community is behind a tab, but once you’re there the navigation reflects the best places to go within the community. The navigation bar appears on the left-hand side on every page. Members can easily browse around and find what they want.
The branding is the same, the community is on the same URL, but the navigation is a lot better. Members can click the Alteryx logo at the top to return to the website.
The Dropbox community and Airbnb community are similar but with one noticeable difference; they’re hosted on their own unique URLs. This enables both (in theory) to create slightly more distinct experiences, but at a cost of search traffic they would be likely to receive if on a subdomain of the main URL. In practice, however, they usually have to adhere to brand guidelines. Thus they get much of the same downsides but without the additional upside.
Unique URLs are often symptomatic of a community with limited internal support. The Dropbox community, for example, is the very last option from the navigation bar at the bottom of the homepage.
The Airbnb host community is almost impossible to find from the community homepage (I’m genuinely not sure how people stumble across it).
As a rule, you generally want the community to be as a subdomain prominently linked to from the main homepage. This subdomain should allow you to create a navigation structure that shows off the best of the community with an easy link back to the main homepage.