John the Ripper is a fast password cracker, currently available for many flavors of Unix, Windows, DOS, BeOS, and OpenVMS. Its primary purpose is to detect weak Unix passwords. It supports several crypt(3) password hash types commonly found on Unix systems, as well as Windows LM hashes. On top of this, lots of other hashes and ciphers are added in the community-enhanced version (-jumbo), and some are added in John the Ripper Pro.
Dar is a shell command that makes backup of a directory tree and files. Its features include splitting archives over several files, DVD, CD, ZIP, or floppies, compression, full or differential backups, strong encryption, proper saving and restoration of hard links, extended attributes, file forks, Door inodes, and sparse files, remote backup using pipes and external commands (such as ssh), and rearrangement of the "slices" of an existing archive. It can run commands between slices, before and after saving some defined files or directories (for a proper database backup, for example), and quickly retrieve individual files from differential and full backups. Several external GUIs exist as alternatives to its CLI interface, like kdar, DarGUI, SaraB, etc.
Lepton's Crack is a generic password cracker. It is easily-customizable with a simple plugin system and allows system administrators to review the quality of the passwords being used on their systems. It can perform a dictionary-based (wordlist) attack as well as a brute force (incremental) password scan, including the use of regular expressions. It supports standard MD4 hash, standard MD5 hash, NT MD4/Unicode, Lotus Domino HTTP password (R4), and SHA-1 hash formats. LM (LAN Manager) plus appending and prepending of characters is available in the Development branch (strongly recommended).
Rsyncrypto allows you to encrypt a file or a directory structure such that they can later be synchronized to another machine using rsync. This means that local changes to the plain text file result in local changes to the cipher text file. rsyncrypto compresses the plain text file prior to encrypting it with gzip using the "rsyncable" patch, which is available from the rsync sources.
Weplab is a tool to review the security of WEP encryption in wireless networks from an educational point of view. Several attacks are available, so it can measure the effectiveness and minimum requirements of each one. Currently, weplab supports several methods, and it is able to crack the WEP key from 600,000 encrypted packets.
The Shrew Soft VPN Client for Unix is a free IPsec Client for FreeBSD, NetBSD, and Linux based operating systems. It can be used to communicate with systems running ipsec-tools. The Unix client utilizes the IPsec kernel support included with the operating system, and comes with the complete Internet Key Exchange daemon and client front end application source code. A Windows version is also available.