LATEST - The latest is under firmware/20191213 - MicroPython v1.11-665-gfb0141559-kaki5
The firmware include LittleFS.
You can use LittleFS instead of FatFS(default) by doing these in REPL:
>>> import os
>>> os.VfsLfs2.mkfs(bdev)
You can download custommade.zip and read this blog to build custom made firmware.
The firmware was compiled without web-repl, upip, and help modules.
Read my blog.