Not only do they share similar qualities, they are practically the same story. Frogman and Amagami revolve around swimming. This boy meets a girl who is the best on the swim team and it is love at first sight. Then the manga develops further into this one-sided romance as the boy joins the team to be with the girl. Both of these manga are heavily ecchified. Lots of bathing suits and soaked women in these two, that is for sure. If you liked on the other is about the same.