LibreSSL Portable

The first portable release was in June 2014. 

Has since replaced OpenSSL in a few linux distros (Arch, Void, etc.)

Significant inroads in other places (It's in many package systems)

Is the default library used in some large organizations.

Portable is getting pretty mature. Hard to find a mainstream os you can't use it on. 

Yes, it works on Windows too.