The stunnel program is designed to work as an SSL encryption wrapper between remote client and local (inetd-startable) or remote server. It can be used to add SSL functionality to commonly used inetd daemons like POP2, POP3, and IMAP servers without any changes in the programs' code. It will negotiate an SSL connection using the OpenSSL or SSLeay libraries. It calls the underlying crypto libraries, so stunnel supports whatever cryptographic algorithms you compiled into your crypto package.
Z1 SecureMail Gateway is a central, server-based software solution that provides encryption and digital signatures (PGP and S/MIME) for the entire email traffic of an organization. It works with organizational certificates and certificates for individual users, groups, or organizational units. It provides its services transparently to end users. Z1 SecureMail Gateway automatically finds certificates of external users or companies via Internet. Secure email traffic to customers, suppliers, and partners is easily established. Evaluation packages for Debian and Solaris are available for download.
CyaSSL is a C-language-based SSL library targeted for embedded and RTOS environments, primarily because of its small size and speed. CyaSSL supports the industry standards up to the current TLS 1.2 level, is up to 20 times smaller than OpenSSL, includes SSL client libraries and an SSL server implementation, includes an OpenSSL compatibility layer, and offers several progressive ciphers such as RABBIT and HC-128. Dual licensed under both the GPLv2 and standard commercial licensing, it caters to a wide range of projects.
PolarSSL is a light-weight cryptographic and SSL/TLS library written in C. PolarSSL makes it easy for developers to include cryptographic and SSL/TLS capabilities in their (embedded) applications with as little hassle as possible. Loose coupling of the components inside the library means that it is easy to separate the parts that are needed, without needing to include the total library. PolarSSL is written with embedded systems in mind and has been ported on a number of architectures, including ARM, PowerPC, MIPS, and Motorola 68000. The source is written to have very loose coupling, enabling easy integration of parts in other software projects. Very loosely coupled cryptographic algorithms for MD2, MD4, MD5, SHA1, SHA-256, SHA-512, AES, Camellia, DES, Triple DES, ARC3, and RSA are included.