AppleTalk is the protocol. The 3-wire (or, later, two-wire over telephone wire -- PhoneNet) networking Apple made ubiquitious for so many years is LocalTalk (which connects to the Mac's serial port).
Note that these are NOT "ordinary" serial ports -- a PC serial port is incapable of supporting LocalTalk.
LocalTalk cards for PCs do exist, but since they were very rare, they are very expensive -- several times as expensive as a LocalTalk-Ethernet converter, which is just $100.
Alternatively, get an old Mac with both LocalTalk and Ethernet, and use LocalTalk Bridge to link them.