Bcachefs

The bcachefs filesystem started out as bcache a blocklevel caching (hence the name) for Linux to allow for faster disks (SSD/NVME) caching slower disks (HDD). At some point, they found out it was almost a filesystem already, so they set off to make it one, adding fs at the end.

The filesystem is currently in development and hasn't been accepted into the linux source tree. It is available for download from their site and from there can be compiled up with the kernel it comes with (5.13.0 at the time of writing) together with the userspace tools, bcachefs-tools. Make sure to read the INSTALL file and install needed dependencies (and if they haven't added it yet, install docutils to get rst2man).