In DOS times you only had one core, so there was no particular necessity for multithreading. Network card drivers were available using the NDIS standard: http://www.freedos.org/wiki/index.php/Networking_FreeDOS_-_N...
DOS games tended to roll their own protocol on top of the raw packet drivers. This is why they were often LAN-only. Generally in the DOS era you didn't have Internet; it existed, but wasn't widely deployed.
DJGPP got some use (see the PCGPE as well), but professional game development tended to use Watcom: http://www.openwatcom.org/index.php/Project_History
In DOS times you only had one core, so there was no particular necessity for multithreading. Network card drivers were available using the NDIS standard: http://www.freedos.org/wiki/index.php/Networking_FreeDOS_-_N...
DOS games tended to roll their own protocol on top of the raw packet drivers. This is why they were often LAN-only. Generally in the DOS era you didn't have Internet; it existed, but wasn't widely deployed.
DJGPP got some use (see the PCGPE as well), but professional game development tended to use Watcom: http://www.openwatcom.org/index.php/Project_History