From Bioware's "about NWN" page:
"Neverwinter Nights (NWN) is a computer game set in a huge medieval fantasy world of Dungeons and Dragons. This role-playing game (RPG) puts you at the center of an epic tale of faith, war, and betrayal.

As a player, you are able to choose what skills and abilities you will develop as you voyage though the complex and dangerous fantasy world of Forgotten Realms. Be a deadly and dangerous Rogue moving through the shadows using stealth and secrecy, be a scholarly Wizard and wield powerful magic against your enemies, be a hulking Barbarian whose lust for battle is matched only by his terrible rage, be an armor-clad Paladin who protects the innocent and vanquishes his foes, be a crusading Cleric who heals the sick and defends the helpless? be all this and more."

License: commercial (~ $10.00 USD)

Additional System Requirements: NWN CD + valid key