When I was a kid software that would "double your RAM" was a thing. I remember thinking it was awesome, and at the same time feeling a huge sense of doubt that you could do that.
Definitely not. DOS had disk compression utilities, but not RAM - there was no reasonable way to accomplish that at the time.
You may be thinking of "memory manager" utilities like QEMM and EMM386 which tried to maximize the amount of conventional memory available to programs (i.e. below the 640KB boundary). These programs worked primarily by causing drivers and TSRs to run in upper memory - they didn't actually provide more memory.
Oh right! I got disk compression and QEMM and EMM386 all mixed together in my now decades old memory (pun kind of intended) of DOS to produce that false recollection.
AI has kinda already gone through that phase, with quantisation you can effectively double your ram with almost no negative effects by going from fp16 to int8.
I’m surprised the concept of drivespace/double space died off. Maybe most files self-compress well from their native app, but I’m sure it’s not universal. OSs don’t seem to offer a prompt to compress relatively unused files and transparently uncompressed them on-demand.