Free! is a school sports comedy anime of 25 episodes by Kyoto Animation; its two seasons, Free! Iwatobi Swim Club and Free! Eternal Summer, first ran in the summers of 2013 and 2014. Though you may have heard of it as “the swimming anime” and it does indeed feature a lot of swimming scenes (and pretty water and intense racing sequences!), compared to other sports series, neither the swimming itself nor its competitive aspect are the focus of the series. The weight clearly lies on the characters’ relationships, so don’t go into the series expecting to learn how to swim or to get fired up over competitive swimming!
Free! is essentially about a small group of high school students who start up a swim club, then go on to participate in tournaments to make their club a success and to recapture past feelings, as four out of the five main characters share a common past. Most of the time, Free! is light-hearted, silly and sugary sweet (its first few episodes are particularly over-the-top), but it is also about bad communication, pent-up feelings, finding yourself and realizing the importance of friendship.
Note that Free! is clearly aimed at a female audience — just look at all the pretty boys, the homoerotic subtext and the gratuitous fanservice. While it doesn’t have much to show in terms of story and character growth, it’s genuinely enthusiastic about what it does and it’s solid entertainment, especially if you like melodrama and self-aware cheesiness in every regard.