OpenSSH is a collection of command line tools to facilitate logins to remote computers within a reliable cryptographic framework. Highly portable and under very active development for over 18 years, it is the de-facto standard for SSH, SCP and SFTP operations from the terminal.
Ranked in these QuestionsQuestion Ranking
Pro One of the most trustworthy development teams on the web
Pro The reference
If you find samples or tutorials about SSH, they almost always refer to OpenSSH.
Pro Standard implementation that documentation for all other tools assumes you have installed already
A lot of other tools (e.g. git) are based on this for file transfer.
Con Command line tool
It can be difficult to use from a command line interface.