SSH implementations
PuTTY
OpenSSH
Free Unix-like resources that run on top of Windows
Vim, an editor that is an extension to
vi.
Cygwin, a Unix system that runs on
top of Windows.
Alternate Operating Systems to Windows
Links to most versions of Linux
OpenBSD, which emphasizes security of the O/S
NetBSD, which emphasizes portability
FreeBSD
Mac OS X freeware
The GNU Mac OS x public archive
Freeware OS X