Adam Engst, writing for TidBITS:
First up—check out this piece I wrote from the 1994 Macworld Expo San Francisco: “RAM Doubler” (10 January 1994). Developed by Connectix, RAM Doubler was one of the most magical utilities of the early days of the Macintosh. As its name suggested, RAM Doubler promised to double the amount of usable RAM in your Mac, and amazingly, it generally delivered.
That was a big deal back in 1994 because RAM was shockingly expensive—$300 for an 8 MB SIMM at a time when I had 20 MB in my Centris 660AV. For $50, RAM Doubler would double whatever you had: 8 MB to 16 MB, or 20 MB to 40 MB. It was astonishing.
I know of RAM Doubler because I heard about it in the past 15 years or so, but since I did not grow up with Macs at all, I have sentimental connection to it whatsoever. Still, such iconic pieces of software always deserve to be remembered.