Valve has just announced that it plans to launch a new service that allows Steam users to send time-limited trials of certain Steam-enabled games they own to others on their friends lists. Menu options for this Guest Pass system will appear on Steam later this week, though they will operate only for users of Valve's closed beta test. Upon conclusion of that closed period, the beta will extend to owners of Day of Defeat: Source, who will be able to send guest passes for that game to their friends. Valve did not specify what other Steam games will be eligible once the full service goes live, though today's announcement did state that it will apply to Steam-enabled games purchased both online and at retail.