This is a maintenance release that adds several new features as well:
Remote file system information in SFTP
Rebex SFTP features
GetFileSystemInfo method, which makes it possible to determine free space and other information about a remote file system drive.
Native elliptic curve cryptography on Windows Embedded Compact 2013
Rebex components utilize MS CNG API on .NET Compact Framework 3.9 / Windows Embedded Compact 2013, making it possible to use ECDH and ECDSA ciphers in TLS/SSL and SFTP/SSH without any external plugins.
For a complete list of changes in 2017 R6.1, see the release history.