When we created Kinja, we created it using Zurb Foundation, a responsive CSS framework. It was at version 3 back then and we used that version for a long time, for so long that Foundation 5 was almost public when we started to upgrade our own instance. Almost, but still not. That's why we started the upgrade process using the already available version 4. It seemed to be a good idea knowing changes from v4 to v5 will be less serious than from v3 to v4 anyway.
However, we needed a codename for the new design. For the Foundation 4 mockups Etele started working on I came up with Phantom and people around really liked it. I didn't tell everyone but I named it Phantom because Foundation 4 can be abbreviated as F4, and then there you are, F-4 Phantom II. When Zurb pushed Foundation 5 live two weeks later, it was an obvious choice to rename the project to Tiger.
At a later point Péter Orosz sent me this piece about codenames and it was pretty interesting to read it. Phantom was a good codename for an in-between product that never went live, while Tiger was also a good codename for something strong and faster, something roaring. Both codenames were emergent. Also the nerd factor was given with these NATO codenames. And now? I hope we'll still be using Foundation when Foundation 6 arrives.