Thieves Guild is a singleplayer mod, which was loosely inspired by Thief: The Dark Project, a game that was originally developed by Looking Glass Studios. In order to play this mod you will need to have Rune, which was developed by Human Head Studios.
nice flags... i don't remember rune having flags...
Thanks! Yes, you are right, Rune didn't come with flags... It's just one of the many new things that you will find in this mod...