Open SSTP Client is an open-sourced Secure Socket Tunneling Protocol¹ (MS-SSTP) client for Android, developed for accessing to VPN Azure Cloud (or SoftEther VPN Server). So no test with other servers is done.
For usage and more details, please visit the app’s project page.
¹ quoting from the Wikipedia article:
Secure Socket Tunneling Protocol (SSTP) is a form of virtual private network (VPN) tunnel that provides a mechanism to transport PPP traffic through an SSL/TLS channel. SSL/TLS provides transport-level security with key negotiation, encryption and traffic integrity checking. The use of SSL/TLS over TCP port 443 allows SSTP to pass through virtually all firewalls and proxy servers except for authenticated web proxies.","categories":["Internet"]}