Hydorah
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A freeware retro sh'mup (STG, horizontal shooter, etc.) before the term "bullet hell" became popular.
It's got the look of Gradius, the weapon selection of Axelay, the branching levels of Darius, the difficulty of R-Type, and a save function for your sanity. A polished product of love made over the course of two years that you can finish in a few hours.
I'm still looking for all the secrets. So far, I only have the astronaut, pink elephant, and flower. =\
(via)