Avernum 3: Ruined World, an HD reboot of Spiderweb Software's old-school fantasy RPG, is out now. It's $18 on Steam and GOG through Wednesday, February 7, and $20 on Humble and Spiderweb's site. There's also a free demo available here.
Spiderweb bills Avernum 3 as the conclusion to the initial Avernum trilogy, but also describes its story as self-contained and approachable for people unfamiliar with the series—which I imagine plenty of people are, given its complicated history.
There are technically six games in the Avernum series (the non-canon Blades of Avernum notwithstanding), which is itself an expanded remake of Spiderweb's Exile series. The first Exile released in 1995, while the original Avernum released in 2000. Avernum 6 released in 2009.
In 2011, Spiderweb decided to reboot the series while leaning even more heavily on Exile. Which leads us to 2012's Avernum: Escape From the Pit, which carries the subtitle of the first Exile game. Avernum 2: Crystal Souls followed in 2015, and now Avernum 3: Ruined World has capped things off. It's complicated, yes, but it works.