Free Spirit is a Tier Two technology that unlocks Temples, expensive buildings built on field tiles worth a large number of points. The number of points each Temple is worth increases over time. Also, Free Spirit unlocks the Disband ability, which allows units to be disbanded to return half their cost (rounded down).
Previously, Free Spirit also unlocked the Scout unit. However, that unit was removed in the Myriad update due to issues with AI players.
Aquarion has the technology Free Diving instead of Free Spirit. Free Diving unlocks movement in ocean as well as Temples and the Disband ability.