As Patrick Klepek points out in his big reveal over on Waypoint, the resolution of the long-running Frog Fractions 2 ARG could be considered a spoiler to some. So, if you don't want to know how to play Frog Fractions 2, don't read further.
People who want to play Frog Fractions 2... hello. What you're going to want to do is go to Steam and grab Glittermitten Grove. This is Frog Fractions 2. Or at least, Frog Fractions 2 is hidden inside of it.
If you have no idea what's going on, here's the gist: In 2012, Twinbeard Studios put out a free web game called Frog Fractions. It purports to be an educational game, but really it's an absurd, free-associative adventure.
In 2014, designer James Crawford ran a Kickstarter campaign for Frog Fractions 2, and since then an elaborate ARG involving other games and physical clues has been leading sleuths closer and closer to the sequel, which was in development alongside the meta game about finding it. It became a running joke that the ARG itself was Frog Fractions 2, or that anything mildly odd was either the game or a hint as to its whereabouts.
Now we know, thanks to Game Detectives: Frog Fractions 2 is hidden in Glittermitten Grove, which released a couple weeks ago. For instructions on how to find Frog Fractions 2 within the game, Kotaku has you covered. I've only played long enough to know that the first method they explain does work, and opens up another game with Frog Fractions-style humor. I'll let you figure it out on your own if you prefer.
For the full story, I do recommend reading Klepek's breakdown of the development of Frog Fractions 2. It's been fun journey.