Fallout New Vegas started life as Fallout 3 DLC

Bethesda was too busy with Skyrim to work on Fallout New Vegas, so turned it into a full game and gave it to Obsidian

Fallout: New Vegas 'Ultimate Edition' Wandering Wastelands in February

Fallout: New Vegas At 10 - The Definitive Game Of War, Greed, and Loss

Fallout 4: five things you need to know about the DLC, Games

Fallout: New Vegas Is About Letting Go

Fallout 3 and Fallout: New Vegas Join the PS Now Library – PlayStation.Blog

Frontier Add-Ons at Fallout New Vegas - mods and community

Fallout: New Vegas – Honest Hearts DLC – Review

Fallout 3 Broken Steel DLC restored for PC

A visual comparison of the amount of quests in fallout 3 compared to new vegas : r/Fallout

Fallout 3 - Broken Steel on Steam

Fallout 3: Mothership Zeta - The Pinnacle of Paid DLC