This is a plugin for the Android version of Total Commander. As a standalone app, it is inoperable. However, if you do not use Total Commander, it is not suggested to use the app. SFTP servers can be accessed by using this plugin (file transfer over SSH secure shell). Use the additional FTP plugin available from the Play Store if you want to use FTPS (FTP over SSL). 

The fact that it provides the free sshj library for ssh connections is the reason why this plugin is so large. It must additionally include the BouncyCastle project's libraries in order to provide authentication using client certificates.