Not stable or tested enough yet.
People, stop suggesting LibreSSL. One can seriously fuck up his/hers system by replacing a core library by an unstable solution.
Once LibreSSL is proven not to be dangerous, it can be used instead of OpenSSL
Not sure where you've gotten "unstable" from, but I suspect you just didn't inform yourself before posting. LibreSSL is a new fork, yes, but it's beyond the "unstable" phase. The current version of OpenBSD has entirely replaced OpenSSL with their LibreSSL project, not just for the OS portion, but consequently also for every single package in the ~9000 items large repository making use of OpenSSL. All of it works, and it's stable.
That said, there are still a few odd cases of badly written OpenSSL-centric software that needs reworking before it's even possible to link against LibreSSL. This is a different matter.