The first Sony cassette recorder, launched after some lengthy negociations with Philips regarding the royalty fees to adhere to Philips' would-be standard.
Being the industry major it already was, Sony asked to lower, and lower more, said royalty fees. Then threatened to go with Grundig's other would-be standard, the DC cassette.
Philips finally accepted Sony's offer which wasn't really one : no royalties at all ! And a worldwide, successful, long-running standard was born.
You may read a somewhat politically correct, sanitized, version of this at Sony's own website.
The TC-100 still is monophonic and has a frequency response that tops at 10Khz but, surprisingly, the resulting recordings don't sound all that horrible !
However, emphasis was on the accepted worldwide standard (previsibly), portability, long recording time in a compact, easy-to-handle cassette with no threading or bulky reels to carry around : "Sony-O-Matic", the names says it all.
Available as accessories were a footswitch, a handy remote control with a microphone included, a mic mixer from earlier days (MX-600M), and a NiCad rechargeable battery pack. And a nice imitation leather carrying case. And even an in-car adaptor !
The TC-100 is a bit of a missing link between Philips' 1963 ameliorated dictaphone (5Khz response) and the high-end recorders of the early 1970s such as the harman/kardon TC1000 or Sony's own TC-177SD heavyweight.
At 1,75kg (batteries included !), 30 minutes of recording per side and ten hours of recording autonomy, the TC-100 could really damage the low-end reel-to-reel market. And it did.
Updated as TC-100A in 1968/69 with minor differences, the TC-100 garnered a japanese Good Design award.
A still functional and very cute retro thingy I do own, along with the later TC-K88B, TPS-L2, TC-20F, TC-FX7 and TC-FX1010.