Source
You can download the source tarballs here.
The new releases from 0.11.0 are signed with a new gpg key (88A228D89B07C2C77D0C780903D5DF8CFDD3E8E7), which you can find here or on any keyserver.
The older releases before 0.11.0 are signed with the gpg key (8DFF53E18F2ABC8D8F3C92237EE0FC4DCC014E3D), which you can find here or on any keyserver.
Linux
Fedora: dnf install libssh-devel
openSUSE: zypper install libssh-devel
Looking for the latest release for openSUSE? You can find it here.
Debian or Ubuntu: apt-get install libssh-dev
Looking for a PPA for stable releases on Ubuntu? Look here.
Windows
Use vcpkg from Microsoft:
vcpkg install libssh
Git it
You can get the latest version of the master branch as zip and tgz.
You can get the latest version of the stable-0.11 branch as zip and tgz.
Clone it
git clone https://git.libssh.org/projects/libssh.git libssh
To start with git take a look at the Git Community Book.
Browse it
You can browse it here.