Flowers for Algernon has genre Speculative fictionSpeculative fiction has examples: Zoe's Tale
[Human]: Can you recommend a book similar to Flowers for Algernon? [Assistant]: The Secret Garden is another great book like that one. [Human]: Sounds good, what genre would that be? [Assistant]: Oh sorry, its Speculative Fiction [Human]: I think Zoe's Tale is speculative fiction too. Can you recommend anything else? 
Sure! You might enjoy The Great Gatsby, which is also a Speculative Fiction novel.