Green Stars had their debut in Super Mario Galaxy, but they didn't play nearly as big as a role in that game as they did in the Sequel to Galaxy, and the eventual successor, Super Mario 3D World. SM3DW took a different approach as a Star Coin replacement, but Galaxy 2 used it as post-game content to extend the story some more, which results in being able to double your star count compared to the previous 120 stars that were required to unlock the Green Stars.
However, a hacker that goes by the name of "Arthurtilly" took to hacking the entirety of Super Mario 64 to include these Cosmic Gems. Right off the bat, you'll realize that you can enter any stage in any order, with later stages having harder difficulty stars to collect. If you think you can just go defeat Bowser immediately, then you'll realize that the pipe to the final fight is blocked with a Star Limit. You must collect all previous 120 stars to access the fight, plus a fully-custom bonus level.
If you would like to play this hack, you can follow this link, or just simply search "Super Mario 64: The Green Comet" to be led to a release trailer.
Super Mario: Star Road is a timeless classic made by the well-known ROM Hacker "Skelux". It's initial release date was around December 2011. Ever since it came out, it's been played by many and loved by almost all players. This major hack contains 130 stars to collect, with 10 of them being called "Replica Stars", where once the player collects 121 stars and climbs the finale stage, Yoshi will inform the player that they can search previously explored levels for the Replicas as an extra challenge. For comparison, vanilla Super Mario 64 contained 120 stars.