Guild Wars 1
This is the original Guild Wars, predecessor to Guild Wars 2.
You can buy it on Steam as "Guild Wars Trilogy", sans the Add-On Eye of the North.
Add-Ons
The original game is called "Prophecies" or "Vanilla".
There are three Add-Ons: Factions, Nightfall and Eye of the North. Only the former two are included in Steam's "Trilogy".