When the PS4 launched on November 15th, 2013, the free-to-play MMO-ish shooter Warframe was available to download. It had debuted on Windows the previous March and came to Xbox in September 2014, yet still sustains a healthy playerbase. The Warframe team has been refining it since, adding content for free. Now, its latest gratis expansion is live on the PS4 version.
Warframe procedurally generates maps whenever a player embarks on new missions. The expansion, Plains of Eidolon, adds a large new area that players share, a la most MMOs. While it probably won't compare with grander paid, games, the new content might be worth looking into if Destiny 2 is no longer scratching your sci-fi shooter itch.