It’s been exactly 10 years and 6 days, but I clearly remember the day of the IV Calculator’s inception. Well, the online–only version was a couple of months older. Since then it’s been updated for 19 games across 4 generations and translated to several languages. The latest update incorporates all hidden legendaries and forms from Pokémon X & Y, including Diance, Volcanion and Hoopa.
Last but not least, the calculator has made the jump to GitHub, where detailed documentation and extra material shall follow; when time allows it. That of course means, that you can Pull Requests if you spot a bug or come up with an improvement.