MoofTCP
MoofTCP is an MIT-licensed, from-scratch TCP/IP stack in portable C that replaces MacTCP for 68k Macs running System 6. Existing MacTCP applications can use it unchanged; it includes a control panel and a basic DHCP client.
The author tested it on a 4 MB Mac Classic and in an emulator. It needs an existing compatible Ethernet driver, has no IPv6, and its DHCP implementation has known gaps. In the HN thread, a reader asked for comparisons with MacTCP; the author shared preliminary latency and throughput figures, while another reader cautioned that the gains looked marginal without memory comparisons and error bars.