OS X RDP server application I am searching for a RDP implementation on OS X, but can't find any. 

Does OS X have an RDP implementation application?
I, too, was a loyal user of iRAPP. CodeRebel is still in bankruptcy as of today. There's a new company, https://www.nuords.com/, that the CTO of CodeRebel has co-founded to sell comparable technology. I have not tested this product; I don't know whether the IP issues have been resolved.

xrdp works on Sierra (I'm using it right now). The compilation instructions can be found on these two pages:

https://github.com/neutrinolabs/xrdp/wiki/Building-on-OSX-(not-official)
https://github.com/neutrinolabs/xorgxrdp/issues/78

The instructions work with macports as well as homebrew; on macports, the final package you need is pkgconfig rather than pkg-config, and you don't have to work around the absence of OpenSSL. It took me about 15 minutes from start to finish to get it running.