OpenSSL is a free, open-source toolkit that can be used to create SSL certificates. SSL certificates are used to digitally identify companies and organizations on the Internet, and to securely encrypt communication and transaction with servers operated by the organization owning the certificate. The fact that OpenSSL is free and open-source implies that anyone may use OpenSSL to encrypt his communication and online activities on the Internet, thus safeguarding individual privacy and personal information from hackers and online thieves.
You can compile the OpenSSL library for the Windows operating system by using freely-available MinGW and MinGW-w64, as shown in this post and this post. This makes it possible to create self-signed certificates for Apache Web servers and email servers running on the Windows platform.