btoa
Binary to ASCII: a 1980s Unix encoder that packed four bytes into five characters and so wasted less than uuencode.
Email and Usenet were both built for text, so binaries had to be re-encoded before sending. uuencode turned three bytes into four characters, roughly a third more. btoa used base 85 instead, four bytes to five characters, for 25 percent. A block of all zeros was written as a single z. The decoder was called atob, and the output was framed by lines such as xbtoa Begin with a checksum at the end.
btoa never spread as widely as uuencode, mostly because everyone already had uuencode. The idea lived on anyway: Adobe's Ascii85 in PostScript and PDF is a variant of the same encoding. Anyone assuming JavaScript's btoa() is related will be disappointed — that one does Base64.