KpyM Telnet/SSH Server
KpyM Telnet/SSH Server is open source. It uses the BSD license.
The downlaod URL is http://www.kpym.com/2/kpym/download.htm and the license can be viewed there.
There is not GUI interface for it. Neither a GUI configuration.
The password authentication is straightforward but the public key authentication is somehow strange. How to use the public key authentication is described in their forum. You need to add the public key into a configuration file c:\program files\kts\publickey_logon.ini. And you also need to write the login credentials (username and password) together with the public key. It seems the software does not really do the public key authentication. Instead, it uses the public key to find the password in the configuration file and authenticate the user with the password. The big problem is that the password must be in clear text in the file.
Copssh free version
Copssh comes with a free version and a commercial version. The free version can be downloaded at https://www.itefix.net/content/copssh-free-edition.
The free version does not support Windows Server. And it allows only one local user.
It has a GUI for the configuration. You can add users there and set up public key authentication etc.
freeSSHd can be downloaded from http://www.freesshd.com/?ctt=download. Although it is free to use, the source code is not free. The license information is found here http://www.freesshd.com/?ctt=terms.
A step by step installation and configuration document can be found on IBM's: ftp://ftp.software.ibm.com/software/iea/content/com.ibm.iea.wpi_v6/wa/6.2/FTP/WBPMv62_IEA_AdapterInstallConfigureSSHServerLab.pdf.
It has a GUI setup and we can also use the public key authentication. They are all written in detail in IBM's document.
Their website promotes a commercial product with source code, which they claim contains the source code of freeSSHd.