Tilesets - Free (Requires Attribution)
Tilesets - Other
- https://itch.io/c/1904339/gathertown-compatible-32x32-tilesets !!
Tiled - Background Editing
Tiled is a mapmaking program used by lots of game studios. It's the best program to use for Gather right now. Additionally, Gather's open Map/Art git repository has Tiled tile-sheets that are maintained by Gather's art team.
Join the Tiled Discord for help on using the program!