I recently mentioned the new schannel support for libcurl that allows libcurl to do SSL natively without the use of any external libraries on Windows.
This "getting native support" obviously triggered Nick Zitzmann who stepped up and sent in Secure Transport support - the native API for doing SSL on Mac OS X and iOS. This ninth supported SSL library is now called 'darwinssl' in the curl code base. There have been some follow-up commits too to cleanup things and make use of that API for providing the necessary function calls when doing NTLM too etc.
This functionality is merged in to curl'sÂ master git repository and will be part of the upcoming curl 7.27.0 release, planned to hit the public at the end of July 2012.
It could be noted that if your for example build curl/libcurl to also support SCP and SFTP, you'd be linking with libssh2 for that and libssh2 is still relying on a crypto library that is either OpenSSL or gcrypt so you may in fact still end up linking with a 3rd party crypto library... Nick mentioned in a separate mail how he has looked into making libssh2 use the Secure Transport API, but that he faced some issues regarding big numbers which made him hesitate and consider how to move forward.