SLIP

Serial Line Internet Protocol does essentially one thing: it appends an END byte (0xC0) to each IP packet and escapes any bytes in the payload that happen to look the same. No error detection, no address negotiation, no compression, and IP only. Rick Adams implemented it in 4.2BSD in 1984, and by the time it was finally written down as RFC 1055 in 1988 it was already a de facto standard that the document itself described as "nonstandard".

For many people SLIP was the step up from a shell account to a real internet connection with an IP address of their own, over a modem. CSLIP added Van Jacobson's header compression in 1990, which made interactive sessions bearable at 14.4 kbit/s. PPP took over during the 90s, bringing everything SLIP had left out.