On Linux there is zram which creates a first-priority swap partition that just compresses the pages and keeps them in memory.
It looks like Windows also has memory compression.
I believe that OS X has memory compression turned on by default.
It looks like Windows also has memory compression.
I believe that OS X has memory compression turned on by default.
There is also zswap, which is a transparent compressed RAM cache in front of your cache partition. Most distros have it enabled by default, so make sure you don't use it together with swap in zram.
It isn't just turned on by default, there is no way of turning it off.