Vats of Rats (11 pages, free/pay what you want at DriveThruRPG) is a fun fantasy adventure for the older editions/variants of D&D, but I used Cat Hack (16 pages, same place). To create my solo engine, I changed four lines in Eye of the Dragon/Golden Dragon Fantasy Gamebook #4. I created five first level cat characters.

So, the adventure started when the town Reeve visited the town prison cell and saw the man-rat. He listened to the employee report. His cat Jumper was there too. Jumper joined his four cat friends and they headed north to see if they could fix the problem. They were hit with a heavy rain storm and they took shelter in a cave for an hour. When they got to the cave/dungeon complex, they started looking for the entrance that was used the most. The first room they explored was filled with food. The second room contained a human farmer locked up in a prison cell. In the third room they encountered a rat guard who attacked. He screamed to the get the attention of his fellow rats. The PC cats killed the first rat guard and the one that came running in later. Fluff was damaged and partially healed with the only two healing spells that the two cat shamans had. They discovered a rat secret door and followed it to more rooms and encounters. Another nasty encounter was with the two rat vivimancers (the two bosses). Both were killed, but Fluff went to zero hit points. She did not lose one of her nine lives, but she is now crippled (minus two on Dexterity – permanent). She regained four of her five hit points. They also had to deal with a man-rat. The cats ran into the laboratory followed by the man-rat. The cats jumped up on the tables and started knocking glass vials and jars onto the floor. The liquids mixed together which formed a misty gas which rose up from the floor. This gas stung the eyes. The man-rat cried and the cats were able to escape. Jumper still had the dead vivimancer rat in its mouth. Next, they freed the farmer. They went to his place, had a nice meal, and slept near the warm fireplace. Then next day they encountered a frog creature who did not talk to them. The adventure ended when Jumper gave his owner (Reeve) the dead vivimancer rat body. Give this RPG a try!