Developer-made events (also more commonly known as Dev Events) are a chain of "events" that started during the summer of 2014. Dev Events promote exclusively to famous content creators, and they usually sponsor a company or website.
The first Dev Event was "The Roblox 2014 Summer Games", unlike the Dev Events right now, this Dev Event really didn't sponsor any company or website, nor did the players dislike it, it was a new and first opportunity to Dev Events. Since then most of the events happening on ROBLOX are now "Dev Events". There was one last "Normal-Event" (as of 11/6/15), and that was "The Witching Hour Returns".