Octal was widely used some 50 years ago by Digital Equipment Corp. (DEC) and other companies that had computers with a 12-bit word (e.g. the PDP-8) or other multiples of six, such as 18 and 36 (e.g. UNIVAC 1108). I used both the PDP-8 and UNIVAC 1108 in grad school. Characters in both machines typically used six bits, not 8.
PDP-8 instruction format -- note the bits are numbered 0 -> 11. Bit 0 was the MSB (most significant bit).
DEC had such a hard time giving up octal that all of the documentation for the PDP-11, which was a 16-bit processor, used octal notation rather than hexadecimal. This is the reason that original permission codes for Unix, which first appeared on the PDP-11, use octal. (But by the time the PDP-11 was announced, DEC had at least switched to numbering the bits 15 -> 0).
Some more trivia -- CompuServe, which was a widely used dial-up online service in the 1980's and early 1990's (before being overshadowed by AOL), ran on DEC minicomputers, at least originally. All user ID's were numeric, and at some point I made the observation that they never included any 8's or 9's in them, thus they were in octal. My old CIS ID was 70205.