Tribes Universe offers free download of:

• EarthSiege
• EarthSiege 2
• StarSiege & Starsiege Tribes
• Tribes 2
• Tribes Aerial Assault
• Tribe Vengeance

As an appetizer for Tribes Ascend.

Starsiege: Tribes
Tribes at wikia.

Starsiege Tribes Master Server Home page
Plasmatic's Code Forge

Shifter
Renegades

TribesRPG
Particle's Custom RPG
Mod DB - RPGmod
Tribes RPG

Tribes 2

TribesNext is a community initiative to restore online functionality to TRIBES 2, Dynamix's final entry to the Tribes series. The patch allows players to create new accounts, host and join online servers, and have a generally kick-ass time. TribesNext is completely free.

TribalOutpost.com Everything Tribes. Maps. Scripts. Styles. More.

SHIFTERmod
IronsphereRPG (discontinued)

Tribes: Vengeance

Tribes: Ascend