I found this video via a recent Daring Fireball post, which in turn was commenting on the first of a series on TidBITS looking back into their archive of Mac news items.
RAM Doubler is a single small extension that literally doubles your RAM. It’s not guessing at a 2:1 compression ratio, like Salient’s AutoDoubler and DiskDoubler (now owned by Symantec) — you actually see your total memory being twice your built-in memory. Since RAM Doubler is an extension, there are no controls, no configuration. You just install it and it doubles the amount of application RAM you have available.
A number of people have expressed disbelief that such a feat is possible, saying that they’d avoid anything like RAM Doubler because it’s obviously doing strange things to memory, which isn’t safe. […] > Needless to say, since RAM Doubler has only been out for a few days, we haven’t been testing for long, but I can honestly say that neither of us have noticed anything out of the ordinary during this time.
From a low-level computer science operating systems perspective, the classic Mac OS was dangerously primitive. But from a high-level user interface perspective, it remains amazing. To install RAM Doubler — software that radically changed the way the OS worked — all you had to do was copy one file to the Extensions folder in your System folder. To uninstall, you just moved it out of that folder. That’s it. One file in one special folder and then restart the machine.