Can some explain to me what it is?

This is an entrance randomizer designed by mzxrules. It takes every entrance/load zone and randomizes it to take you to a different location. So, entering the Deku Tree can take you to Gerudo Fortress as an example. The seed that randomizes the entrances is generated based on your filename.

Where can I get it?

Just click on the Resources here, I think it’s up to date.

Or, alternatively, I believe there’s a link in the OOT discord.

Thanks, bro.