https://en.wikipedia.org/wiki/Zram
zram, formerly called compcache, is a Linux kernel module for creating a compressed block device in RAM, i.e. a RAM disk with on-the-fly disk compression. The block device created with zram can then be used for swap or as general-purpose RAM disk. The two most common uses for zram are for the storage of temporary files (/tmp) and as a swap device. Initially, zram had only the latter function, hence the original name "compcache" ("compressed cache"). Unlike swap, zram only uses 0.1% of the maximum size of the disk when not in use.[1]
Open-source RAM is better.
It's a compressed RAM drive being used as swap backing. The kernel's already got the functionality to have multiple tiers of priority for storage; this just leverages that. Like, you have uncompressed memory, it gets exhausted and you push some out to compressed memory, that gets exhausted and you push it out to swap on NVMe or something, etc.
Kinda like RAM Doubler of yesteryear, same sort of thing.