Owl (Openwall GNU/*/Linux) is a small security-enhanced Linux distribution for servers. Owl also makes a good base system for customized virtual machine images and embedded systems, and Owl live CDs with remote SSH access are good for recovering or installing systems (whether with Owl or not). A single Owl CD includes the full live system, installable packages, the installer program, as well as full source code and the build environment capable of rebuilding the entire system from source. Owl supports multiple architectures (x86, x86-64, SPARC, and Alpha) and offers some compatibility for packages developed for other Linux distributions. The primary approaches to security are proactive source code review, privilege reduction, privilege separation, careful selection of third-party software, safe defaults, and "hardening" to reduce the likelihood of successful exploitation of security flaws.
blueflops is a two-floppy Linux distribution with a graphical Web browser (links) and an IRC client (rhapsody). The kernel has most of the Ethernet drivers compiled in as modules (including the PCMCIA ones) and PPP support (for dialup connections). The browser is linked with OpenSSL. The scripts are all accessible by a setup script and have a nice dialog frontend.
Thinux is a thin-client server on a live CD. It boots a network of diskless computers to automatically start an application such as a Web browser. Each thin client machine acts as a cluster node to share its processing and memory resources with each other to take the load off the server. It is a turnkey solution that does not change nor rely on your existing systems to run. By booting from a removable CD, it does not lock-in the user so it is convenient to test. It is ideal for any organizations that require large deployment of software automatically and cost effectively.