Here is the full list of all 28 Intergalactic Taxi Co. achievements.
Finish Intergalactic Taxi Co.
Reach Level 100.
Drop off 500 passengers.
Visit the mechanical planet 100 times.
Visit the crystal planet 100 times.
Reach Level 75.
Visit the desert planet 100 times.
Unlock the bus.
Visit the lava planet 100 times.
Visit the icy planet 100 times.
Drop off 300 passengers.
Reach Level 50.
Click on a UFO 10 times.
Visit the grassy planet 100 times.
Use a hint 100 times.
Re-fuel 50 times.
Reach Level 25.
Drop off 150 passengers.
Use a hint 50 times.
Click on the Hula girl in the level select menu 10 times.
Click on the taxi or bus 10 times in a row.
Click on the sun 10 times.
Drop off 50 passengers.
Complete a level using only hints.
Restart a level 100 times.
Restart a level 50 times.
Restart the same level 10 times.
Finish a level without restarting or using a hint.