On many of my posts here I've talked about the RoosterTeeth company in Austin, Texas as they are one of my favourite online industries because of their use of humour and brilliant machinima episodes such as their popular web series, Red vs Blue.
A machinima is were someone uses a game engine to recreate scenes of their favourite movies or (in the case of RoosterTeeth) to make brand new shows with new story lines, plots and characters. The use of these storylines and these characters make intresting episodes, popular with people as they use games which as popular to most people. For RoosterTeeth, they use the Halo series engines to create these storys. Halo was an extremely (as still is) popular video game released for the Xbox by Bungie in 2001.
After Red vs Blue became popular, other people saw the idea of using a game engine to create new stories and episodes. Some even used a mixture of real life shots with game action which was also popular (such as the Arby n' the Chief webisodes)
These games within games are extremely popular as it uses an engine available to everyone which allows anyone to be able to make one if they had the right story. That is one of the reasons why this series became so popular - its ability to be done by everyone.
Just to finish, this is my favourite part of the RvB Series: