In late 2006, I wanted to add SCP and SFTP support to curl. I investigated the library situation for SSH support and I found that there existed two similar Open Source library contenders for this purpose, confusingly similarly named too: libssh2 and libssh.
I wanted the SSH library to work with a non-blocking API to suit curl proper, so I reached out to both the SSH library projects I had found and asked them about their current support and how they viewed the future and offered to work on providing such API and functionality myself. I thought the by far most promising and friendly response came from libssh2, so I made my choice.
In November 2006 we started to add support for SCP and SFTP to curl based on libssh2, and at the same time I started contributing improvements in the libssh2 project. In particular to make sure the API could be set to and behave in a non-blocking way.
libssh2 was founded by Sara Golemon in 2004 and she was still the lead developer when I joined the project but I soon became a co-maintainer and when Sara changed jobs in 2007 she was prohibited to contribute to the libssh2 project anymore and I became almost the primary maintainer.
I am still a maintainer of the libssh2 project in 2022, but I try to keep my activities to a minimum. Others do the real work there now.