XData from ISAPI/CGI

I see. Http.sys does support SNI. I'm not expert in other features of IIS to be honest, but isn't it possible to integrate both (like forwarding requests from IIS to http.sys module)?

Also, I believe most features are available at a lower level in http.sys, like tracing (for example, see here: https://blogs.msdn.microsoft.com/wndp/2007/01/18/event-tracing-in-http-sys-part-1-capturing-a-trace/.
But well, I understand your request, but unfortunately we don't provide an ISAPI module for TMS Sparkle. What does exist right now is a WebBroker adapter so that you can build a WebBroker module (for Apache) and forward the requests to a Sparkle module. Adapting it to an ISAPI module should be relatively easy, but we never had such request before. That would allow you to build an ISAPI module using WebBroker and forward the requests to the Sparkle module in-process. More info about this WebBroker + Apache integration here: http://www.tmssoftware.biz/business/sparkle/doc/web/apache-based-server.html