InterNestor Lite is a TCP/IP stack that works on MSX2/2+/Turbo-R with at least 128K RAM. It supports two kinds of hardware: serial port (RS-232) with modem, and the Ethernet UNAPI.
The sources are intended to be assembled with the MSX assembler Compass, however you can compile them with Sjasm 0.39h
-c switch (which enables the Compass compatibility mode). Example using the Windows command line:
sjasm -c inl-tran.asm inl-tran.dat sjasm -c inl-res.asm inl-res.dat copy /b inl-tran.dat+inl-res.dat inl.com
Binaries, documentation and more resources are available at Konamiman's MSX page.