OpenCola is an actual brand of cola that was founded by Grad Conn, Cory Doctorow, and John Henson and is produced in Toronto Canada by the company OpenCola. It's unique because the instructions for making it are freely available and modifiable under the GNU General Public License.

You can make it and even sell it yourself. Here's the flavoring formula:

10.0 g food-grade gum arabic
3.50 mL orange oil
3.00 mL water
2.75 mL lime oil
1.25 mL cassia oil
1.00 mL lemon oil
1.00 mL nutmeg oil
0.25 mL coriander oil
0.25 mL neroli oil
0.25 mL lavender oil

For more information, visit the OpenCola Wikipedia page