Xbox and PC game Titanfall was originally prototyped running on a Ratchet & Clank engine, it was revealed in journalist Geoff Keighley's newly released The Final Hours of Titanfall feature. In the extensive and fascinating feature, it's revealed that Insomniac Games founder Ted Price called Respawn Entertainment cofounder Vince Zampella in July 2010 to tell him he could freely use Insomniac's "Luna" engine to make the game that would become Titanfall.
Price and Zampella were already friends and were both in similar situations, working on games to be published by Electronic Arts. (Insomniac's game was the co-op shooter Fuse). Because of their existing friendship and because Price wanted to help Respawn succeed, he offered up the engine, which powered Ratchet & Clank: A Crack In Time, and Respawn prototyped Titanfall--then known as R1--for a period of one year using that technology.
It's also revealed in the feature that EA offered to let Respawn use the technology behind Lord of the Rings Conquest and The Saboteur from the since-closed studio Pandemic Studios. Respawn also considered using Epic Games' Unreal Engine, but decided against it because developers feared they would not be able to achieve 60fps in that engine. EA finally switched over to Valve's Source Engine, which runs the final version of Titanfall.
The Final Hours of Titanfall also touches on many other interesting facts about the game's development. It's revealed in the the feature that after learning the specs for Microsoft's Xbox One, Respawn reached out to Sony in hopes of finding out how the PlayStation 4 would compare. However, Sony was not willing to talk specs yet and instead offered to help Respawn make a PlayStation Vita version of Titanfall. That, of course, never happened.
We also learn in the Titanfall feature that the version of the game you know and (maybe) love today wasn't always structured as you now know it. In fact, in an earlier version of Titanfall, players would begin rounds in titans, only to transition to a pilot as an "extra life." But in February 2013, just 13 months out from release, Repsawn changed the game so that you began as a pilot and could call in your titan from above, leading to the name Titanfall.
The full Final Hours of Titanfall hits on subjects like the rift between Respawn founders Jason West (who is no longer with the company) and Vince Zampella that grew as a result of the massive Call of Duty lawsuit, Titanfall's prototyped single-player mode, and how the game came to be an Xbox and PC exclusive. It also features some neat concept art of the various in-development versions of Titanfall, and shows off some early prototype videos of the game.