Ortachala, 2.5km southeast of the Old Town, has services for Kakheti, Armenia, Azerbaijan, Turkey, Greece and Russia. Marshrutky to destinations in Kakheti, and Zaqatala and Qax in Azerbaijan, leave from out the front; other services, including comfortable Metro Georgia buses to Batumi, go from inside.
You can reach Ortachala on bus 50, 55 or 71 from Baratashvili in central Tbilisi. Heading into town from Ortachala, catch these going to the left on the street outside. Marshrutky 108 and 150 run between Ortachala and Didube.