OpenSMTPD is a FREE implementation of the server-side SMTP protocol as defined by RFC 5321, with some additional standard extensions. It allows ordinary machines to exchange e-mails with other systems speaking the SMTP protocol.

Started out of dissatisfaction with other implementations, OpenSMTPD nowadays is a fairly complete SMTP implementation.

The SPICE client provides access to a remote machine's display and devices.
The SPICE server library is used by virtualization software (eg kvm) to expose
a (virtual) machine's display and devices to a SPICE client.

headers defining SPICE-protocol