I was looking at my NeXT software, and I noticed that NeXT had a naming scheme for codenames / internal names for software. It was a word and a number and letter. So, I decided to create a list of all of them. If I'm missing one or you know that one that is wrong, feel free to post and let me know.
NEXTSTEP
0.8 => Photon
0.9 => Kodak (0.94)
1.0 => ?
2.0 => ?
2.1 => ?
2.2 => ?
3.0 => ?
3.1 => ?
3.2 => ?
3.3 => Lightning9I
4.0 => ? (beta)
OPENSTEP Mach
4.0 => Lantern3V1
4.1 => ?
4.2 => Lantern5V
OPENSTEP NT
4.0 => ?
4.1 => Bastion4R1
4.2 => Bastion5U1
YellowBox
5.0 => YellowWin321Z1 (DR1)
5.1 => Pluto1W1 (DR2)
5.3 => ? (1.0)
OPENSTEP Solaris
1.0 => ?
Rhapsody
5.0 => Grail1Z4 (DR1)
5.1 => Titan1U
5.2 => (never released)
5.3 => Hera1O9 (OSX 1.0)
5.4 => Loki1A2 (OSX 1.0.1; mislabeled Hera1O9)
5.5 => Loki2G1 (OSX 1.0.2; labeled Hera1O9+Loki2G1)
5.6 => Pele1Q10 / Medusa1E3 (OSX 1.2 / 1.2v3)
I'll have a look later today (boot up some older systems), but for the internal releases they often used things like 'Fuscia' as well.