Final Fantasy X

The tenth entry in the Final Fantasy series and the first one on PlayStation 2. Visually impressive, and the first game in the series to use voice acting, it also featured a much more refined battle system emphasizing teamwork, and an innovative, yet surprisingly not irritating, stat/character growth system. The downside is that the game was incredibly linear, with most of the game simply involving walking down a very long straight line. It was also the first Final Fantasy game to feature a direct sequel, the very awkwardly-named Final Fantasy X-2.

Unused music
There are a number of unused songs in FFX. Interestingly, three of them appear to have been composed by one each of the game's three composers.

Wakka's Theme


This is the most well-known of the three unused songs, as it's an unlockable bonus track on the in-game music test. However, it's never heard in the game proper. Its intended usage is pretty obvious, but "Blitz Ball Gamblers" is always used in Wakka-centric scenes. Given its similarity to the music from Final Fantasy IX, it's likely this song was composed by Nobuo Uematsu.

Nostalgia


This song, however, is not included in the in-game soundtest, and is entirely unused. Sounds rather melancholy; likely intended for serious/sad cutscenes. It's very similar to Masashi Hamauzu's other contributions to the FFX soundtrack, and was probably composed by him.

Illusion


A peppy, yet mysterious-sounding song that'd feel right at home in Threads of Fate, whose soundtrack was also composed by Junya Nakano. No idea where this would've fit in, but it's not on the in-game music test, either.

Hum of the Fayth (Female)


Tidus hums the Hymn of the Fayth at one point, but this alternate female version is never heard. It's unclear whether it's Yuna or Rikku humming this version, however.