UDPCast allows to send data simultaneously to many destinations on a local net. This can for instance be used to install entire classrooms of PCs at once. The advantage over using other methods (nfs, ftp, whatever) is that udpcast uses Ethernet's multicast abilities: it won't take longer to install 15 machines than it would to install 2. The tool comes with a busybox bootdisk for easy loading of the tool. However, udpcast can also be started from the command line of an already installed system, and can be used for other purposes than just system installation.
scponly is an alternative "shell" of sorts for system administrators who would like to provide access to remote users to both read and write local files without providing any remote execution priviledges. Functionally, it is a wrapper around the ssh suite of applications. It is typically used by creating a user whose shell is set to scponly. This user can neither login interactively nor execute commands remotely, but it can use scp and sftp to download and upload files to the computer, governed by the usual Unix file permissions.
queue_repair can be used to check or correct most corruptions of the queue in qmail (resulting from filesystem damage, etc). Functionality includes automatic, dynamic determination of UIDs and GIDs. Automatic, dynamic determination of use of big-todo. Handles basic tasks like fixing a queue restored from backups, incorrect ownership or permissions of directories and files, missing or extra split subdirectories, unexpected files or other directories, or creating a valid queue from scratch.
The IP Masquerade HOWTO is the document that contains instructions on understanding, configuring, and troubleshooting NAT or Network Address Translation for Linux. It covers topics such as IPTABLES, PORTFW, IPCHAINS, IPFWADM, stronger packet firewalls, multiple network segments, and configuring many client operating systems. It also has an extensive FAQ and troubleshooting section.