BasicLinux is a mini-Linux distribution designed specifically for old PCs. It provides a slim 2.2.26 kernel, a user-friendly shell and a good assortment of utilities. It includes a Web browser, a comm program, an email client, a telnet client, wget, DHCP, and dial-up PPP. It also includes a small footprint GUI, and is able to run remote X (via network) with as little as 4 MB RAM. BasicLinux is particularly suitable for old laptops: it comes with PCMCIA capability and includes the MagicPoint presentation program.
eCos (Embedded Configurable OS) is an open source, configurable, portable, and royalty-free embedded Real Time Operating System. It is written in C++, provides all the usual OS things. You configure the OS so that the parts you don't need aren't loaded to the embedded system. eCos is released under a modified GPL that allows for its use in embedded systems without having to GPL the embedded application.
fli4l is a single-floppy Linux-based ISDN/DSL/ethernet-router. It features configuration with some simple ASCII-files, several possible connection-flavors (in/out/callback, and raw IP/PPP), channel bundling (an extra channel can be added through a Windows/Unix-client), configuration of multiple networks, least-cost routing, automatic choice of provider, display/calculation of connection times and costs, and a Windows/Unix client to control dial/hangup, monitor traffic and monitor incoming calls on ISDN (see screenshot).
Briefly, FreeBSD is a UNIX operating system based on U.C. Berkeley's 4.4BSD-lite release for the i386 platform (and recently the alpha platform). It is also based indirectly on William Jolitz's port of U.C. Berkeley's Net/2 to the i386, known as 386BSD, though very little of the 386BSD code remains. A fuller description of what FreeBSD is and how it can work for you may be found on the FreeBSD home page.
Inferno was originally developed at Bell Labs (the research division of Lucent Technologies). It is a well-designed, economical operating system particularly suitable for use in networked devices such as advanced video telephones, hand-held devices, TV set-top boxes, and many other embedded applications. Inferno can run in native mode on an embedded system or in emulation mode under many different operating systems. Inferno has many features in common with Plan 9.
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.