Lilac

I love Cassette Beast! It's fresh and definitely unique. The premise is that you go around recording 'pokemon' with cassettes, and that very cassettes will later be used to transform yourself into the 'pokemon' you recorded!

People might say go for Coromon, but it feels more like a beat-to-beat copy. But there are a few more alternatives like Monster Sanctuary, etc. Go to GameWhims and you can find a full list of pokemon-like game!