These game engines were normally just distributed to developers in the same company and never released to other development studios therefore these are called ‘in-house’ game engines.
Game engines have always been used to a certain extent within the games industry for re-using code from one game to another. When the Xbox came out in 2001 most game developers were still getting used to the new layer of abstractions and code re-use provided by the superior hardware of consoles compared to the previous generations. Original Xbox Game Engines Edit on Github
