Finally I found my spare Humble Indie Bundle #2 key. This time i decided to give it not random, but for knowledge (or google skill). To win you need to answer simple question:
What is common between
Flamingo
Crocodile
Frog
Zippo
Satan
Wasp
Sea Serpent
Ronson
Badger
?
(and yep, it is slightly incorrect:))

Finished.

They're tanks!! :D

Edit: flame tanks?

Yep flame tanks looks right to me. Good call.

The only thing I can find are (flame) tanks and such, from a mod for Men of War.

Another possible answer: they're all on this thread.

Tracked vehicles with flamethrowers in WW2. Congratulation! Check PM:)

I didn't know about HIB when this 2nd bundle was being sold, and I own none of those games. Thanks a bunch!!!