Dating sim hacked
If you gave the girl enough emeralds, it wasn't too hard to enter the Macro side of the game, where you had an interactive sex scene, like the hotel, but with the Macro version of the girl or guy.
The game had a number of endings like the girl not growing, the girl growing but ending up killing you etc, which all depended on choices and how well you did in the game.
Dunno if I'm just lazy, but I wish the stats were at max first and not us clicking them 356 times.
Other than 'stolen' copies of the game, rumours are that a 'hacked' version of the original release is floating around which increases Rouge/Shadow encounters and is far from supported by the creator.
Many 'spam' sites have taken the name of MSDS in order to get people to their sites, showing that the game is probably a lot more popular than believed by the creator.
Different ones of the four girls (Amy Rose, Tikal Echidna, Princess Sally Acorn & Sonia Hedgehog) and three boys (Sonic, Tails & Mighty) would appear at different locations in patterns which could be easily worked out with a bit of skill.
Once in a while, an Event would happen that would give you a big boost with the girl/guy of your choice or a Chaos Emerald would appear.