"Speak Freely is a public domain, cross-platform Internet telephony application which conforms to all relevant standards, implements most principal audio compression algorithms, and provides military-grade encryption with AES, Blowfish, IDEA, and DES with keys as long as 256 bits.
Speak Freely is available for Unix-like platforms (Linux, FreeBSD, Solaris, IRIX, etc.) and Windows machines. Both versions are completely compatible and interoperate. In addition, Speak Freely supports the RTP and VAT protocols, and can communicate with any compliant Internet audio application. "