What was the app after the second app released by YouTube?

Context: Through this period, YouTube tried several new ways to generate revenue beyond advertisements. In 2013, YouTube launched a pilot program for content providers to offer premium, subscription-based channels. This effort was discontinued in January 2018 and relaunched in June, with US$4.99 channel subscriptions. These channel subscriptions complemented the existing Super Chat ability, launched in 2017, which allows viewers to donate between $1 and $500 to have their comment highlighted. In 2014, YouTube announced a subscription service known as "Music Key," which bundled ad-free streaming of music content on YouTube with the existing Google Play Music service. The service continued to evolve in 2015 when YouTube announced YouTube Red, a new premium service that would offer ad-free access to all content on the platform, premium original series, and films produced by YouTube personalities, as well as background playback of content on mobile devices. YouTube also released YouTube Music, a third app oriented towards streaming and discovering the music content hosted on the YouTube platform.

Answer: The third app released by YouTube was YouTube Music, which oriented towards streaming and discovering the music content hosted on the YouTube platform