The Citadel, The Military College of South Carolina | The Citadel | Citadel Broadcasting | citadel | The Citadel (military college) | Citadel | Citadel Miniatures | Alcatraz Citadel | Warsaw Citadel | Royal Citadel, Plymouth | Citadel of Salah Ed-Din | Citadel Communications | The Citadel (novel) | the Citadel | Spandau Citadel | ''On the Way between Old and New Cairo, Citadel Mosque of Mohammed Ali, and Tombs of the Mamelukes'', by Louis Comfort Tiffany | Citadel of Lille | Citadel of Besançon | Citadel of Aleppo | Citadel LLC |
Along with its offshoots DOC has inspired at least four clone codebases, including YAWC, which is likely the oldest, Jammin, which has since become WeIrDo, bbs100 (which is licensed under GPL), and A better Citadel (ABC).