The S'Lanter are a race of intelligent FEV mutated raccoons that were cut from the final release of Fallout 1.
The Burrow was S'Lanter's settlement.
This file is a PDF version of the developer documents for this content that never made it into Fallout 1.
It has a lot of backstory and lore about this race, their settlement and their way of life.
It's worth a read if you are interested in cut content or just the S'Lanters.
S'Lanter and Burrows Development Documents 2018-12-05
This is a PDF of the Development Documents for the cut Fallout 1 S'Lanter and Burrows content.