Pklinux-bigi is a Slackware derived distribution based on glibc 2.2 and Linux 2.4.0-test11. It can run on 386, 486, 586, and Pentium machines with only 4 MB of RAM. Builtin features include IP tunneling, firewalling, encapsulation, QOS(based on ipv4 RSVP), kernel debugging, loopback, network block device, and numerous filesystems (including ntfs and sysV). It contains Apache, proftpd, bind 9.0, syslogd, sendmail, iptables, iproute2, and gated. NAT configuration by iptables is included by default. It is a loopdisk based distribution which can be directly run from DOS, no hdd partitioning needed. This distribution is kept as minimal as possible and it can be useful in places where you want a low end computer to act as a firewall, webserver, mail server, router, or an alternative to zipslack.
Pocket Linux is an almost minimal, one floppy linux system designed to quickly convert PC workstation into secure linux-based workstation using ssh to connect to remote host (other networking clients are also supported). It supports bootp for determining host IP and other network parameters (there's also manual configuration possible, but bootp is recommended). In addition to workstations equipped with a network card (ethernet or arcnet), you can also use Pocket Linux on a PC equipped with a modem. Modem is automatically detected and then PPP connection is made.
Open Distributed Data Acquisition System Linux is a mini distribution of GNU/Linux intended for use on the ODDAS project. It contains a shell and some basic commands plus servers for HTTP, FTP and telnet. It also includes the capability to perform syslog over the network, and contains a very simple mail program which allows alerts to be forwarded across the network. The whole thing squeezes into about 3M of flash on an Intel [3-6]86 processor.
Leetnux is a Linux distribution specifically designed for Linux users who want maximum configuratibility. Therefore, the installation is quite hard and absolutely nothing is done "automagically" as in modern Linux distributions, but the user has total control over installation and configuration.
ISDN Router allows you to convert old hardware into a secure masquerading ISDN router, including caching nameserver, IP Port Forwarding, and on-demand channel bundling. The system fits onto a single disk, and users can change the configuration through a simple menu-based system (on the console or over telnet) and store it permanently on the disk.