Thai basil
Thai basil is an aromatic herb used widely in Southeast Asian cuisine. It is definitely different in taste and looks to the sweet Italian basil most are familiar with. You really cannot substitute one for the other.
Sweet basil, is well, sweet. Thai basil on the other hand is more along the lines of licorice, and anise.
The appearance is different too. Thai basil has pointed leaves, and purple blooms, whereas sweet basil has large broad leaves.
Another way in which they are different is in their taste once cooked. Sweet basil is better eaten raw-thin bruschetta, Its flavor looses its brightness once cooked. Thai basil on the other hand, will retain its flavor even after cooking.
If you have a spot in your garden that receives full sun, go ahead and plant this herb. It's easy to grow; trust me I am not a good gardener and this plant does well in my yard.
If you like Southeast Asian cuisine, give growing this herb a try!