Prepare to die, Dark Souls: Prepare to Die Edition.
While the original 2012 released PC port thrived after myriad updates, it's now completely wiped from purchase on Steam to pave the way for the newly minted remaster. You can still download it, you can look at the cool icon of the Black Knight -- you just can't buy it if you're a new potential onlooker.
Instead, you'll be able to pick up the Remastered edition on May 25 when it's released on PC, PS4, and Xbox One (Switch was delayed), which sports dedicated servers and DLC bundled in. As a reminder if you own the Prepare to Die Edition already, you can grab Remastered for half off.
Dark Souls [Steam]