Please clearly & explicitly identify what existing feature of SME server or what existing contrib that you think your request relates to.
I have an SME9 server, in server/gateway mode, acting as router for my home network. I want it to route traffic from one SSID on my WiFi differently from traffic on the other SSID. One SSID should be treated as part of the LAN, with full access to all LAN resources and the ability to see other WiFi clients. The other SSID would be a guest network, where clients can't see other WiFi clients or resources on the LAN. Since routing network traffic is a feature of the SME server, you've frequently expressed the position that anything you can't do by a checkbox or pushbutton in the server-manager (even if it's a supported, templated, and documented configuration for packages installed in the base system, as with DKIM) belongs in the contribs forum, and I don't know of any checkbox or pushbutton in the server-manager that would accomplish this kind of routing, that's where I put the topic.
CoovaChilli looks like it could probably be made to do what I want, though it seems far more heavyweight than I need (I don't have any interest in user authentication for the guest network, nor in restricting which ports or services they can use to connect to the Internet), and I'm not sure if or how it would deal with the VLAN, which I'm assuming is the only way the SME server would know which clients are on the guest network and which on the regular one. If I wanted bandwidth limiting, or a captive portal, or time limitations, or any such thing, I could configure it using the UniFi manager software without involving the SME server. The UniFi manager will also let me configure an SSID to be a "guest network", which apparently (though I haven't found clear documentation of what it does) prevents clients of that SSID from seeing each other. The part that I think requires the cooperation of the SME server is for clients on that guest network to not see or have access to other machines on the wired LAN, like my FreeNAS box.
Now to my question: which part of this was unclear from my original post? I'll admit that I didn't explicitly say that I was using SME as the router, but I think that could have been reasonably inferred from the facts that (1) I posted in the SME9 contribs forum, and (2) I linked to another (very recent) thread where another user was trying to do something similar using SME9 as his router. At a minimum, it should have given rise to a question like "you are using SME to route the traffic, right?", rather than the assumption that someone who's been using SME since before it was SME, and has been active on the forum for several years, has no idea where to post his question.