Helix Swarm has always been free to use with an unlicensed Helix Server. With the 2014.4 release, Swarm is free to use with any Helix Server. You no longer need to purchase a Swarm-specific license, and any existing Swarm-specific licenses are no longer evaluated.
An unlicensed Helix Server provides unlimited use for up to 5 users and 20 workspaces. When the user or workspace limit is crossed, Helix Server imposes a maximum of 1,000 files. Swarm honors the restrictions of Helix Server.