I was scrolling through the metadata options and found Engines & tools - sadly I didn't find the "I made it myself"-engine option.
Now obviously you can leave the field empty to indicate that you didn't use an engine or other tools, but so do all games out there that missed that the option is available.
I would suggest a "I made it myself"-engine using the link in the same page, but some fields (such as Website) don't really makes sense.
Personally I would like to know if the developer made the tech behind the game from scratch, as it tells a lot about the devs. My suggestion is to add a new field indicating this (maybe "home made engine"?).
If you're one of those who also click More information and look at the Made with field, what are your thoughts?