Is there a way to set up a linux based, preferably ubuntu, SSTP server?
I know there is a SSTP client available on sourceforge, but I can't find a server.
To be clear: I do NOT want openVPN, I want SSTP
There is no SSTP server software for Linux currently available. There is an SSTP client available for Linux and SSTP server implementations available for Windows (as Microsoft developed the protocol) and RouterOS. There is an open specification, so there isn't a reason why someone couldn't develop the server. It just hasn't been done.
Some reference links:
The reasons you probably haven't seen much open-source development on this are:
If you want SSTP because firewalls already let through TCP port 443 traffic, OpenVPN already supports running a TCP-based server on any port, including 443. OpenVPN setups using TCP port 443 are quite common for this reason, although they're rightly not the recommended setup because running IP over TCP (especially TCP over TCP) generally gives poor performance.
Yes, there is a Linux (and Windows/Mac) based SSTP (and lot more) VPN Server. It is called SoftEther VPN (http://www.softether.org). I used it on Ubuntu 13.04 release. Best of off, it is free. Granted, there are couple of limitations with the free version (for example, cannot use external authentication, client certificates etc.)
In general, it seems to work fine. It is quite easy to install, use and manage. Has decently good documentation. Has quite a few options. It does serve my SSTP server needs.