If open source isn't a requirement and you want a polished GUI client, https://www.bitvise.com/ssh-client has been free as in beer for about 1.5 years. It will be tough for them to beat being part of the default install!
Bitvise sells a solid Windows-friendly SSH server for $100. I am not affiliated apart from being a happy user since before OpenSSH supported AuthenticationMethods (multiple required) in 2013; it has been my straightforward licensing alternative to Remote Desktop Gateway.
Thanks for pointing this out; I'd forgotten about that (having given up on Putty after discovering the difficulty of sharing configuration https://stackoverflow.com/q/13023920).
Putty.org links to the Putty download page with a disclaimer separating promotion of Bitvise software below. The contrast in marketing language between "source code [...] developed and supported by a group of volunteers" vs. "developed and supported professionally" definitely appeals directly to the Windows mindset! Unfortunately Bitvise's "growth hacking" makes commercial sense, even if it does cost them potential users.
Odd licensing (free for up to 4 users/machines, but crossing to 5 required $45/seat) really crimped adoption before the license was changed. https://web.archive.org/web/20160329203117/https://www.bitvi...
Bitvise sells a solid Windows-friendly SSH server for $100. I am not affiliated apart from being a happy user since before OpenSSH supported AuthenticationMethods (multiple required) in 2013; it has been my straightforward licensing alternative to Remote Desktop Gateway.