clac (Command Line Advanced Calculator) evaluates mathematical expressions input via command line arguments or from stdin and writes the results to stdout. Unlike other command line calculators, clac has infix (natural order) expression syntax, is quite comfortable with complex numbers, defines a great many functions and constants by default, and allows easy definition of new user functions and constants using Python.
Seetxt is a lightweight text file and man page viewer for X windows. It maintains "document meta-data" for each user, allowing them to automatically keep bookmarks and highlights for read-only system files. It also has a "server mode" so that command line requests can be sent to a single running server rather than starting multiple instances. Other features include hypertext-style apropos (man page) searches, file monitoring, multi-level regular expression searching, a command history, and nice little toggle lights on the interface for the server and file monitor. There's also cross-application drag-n-drop support, and handy little features that allow you to view the output of shell commands and process the text buffer with an external command (sed, awk, grep, perl, etc.) Seetxt is POSIX compliant.
Nall is a small status icon application that discreetly fits into the system tray. Its purpose is to spawn a list of user scripts periodically and display one line of output per script in a tooltip window. Thus, it is possible to "monitor" any kind of event that can be detected with a script. Nall does not care about the return values of the scripts it runs, but only displays their output. It is also easy to interface nall with Nagios plugins.
Diskus is a high-level hard drive diagnostic and limited repair tool. It checks the disk geometry by writing numbered IDs into the sectors of the hard drive. Later one can verify that these sector-IDs on the disk are still correct, thereby detecting data which was not correctly written. There is an option to "freshen" the data on your harddrive, which will read and rewrite the sectors. With modern drives this will re-map defective sectors.
Artha is a handy thesaurus based on WordNet with distinct features like global hot key look up, passive desktop notification, regular expression based search, etc. Artha may be used as a free open-source replacement/clone to the proprietary WordWeb Pro thesaurus (which is also based on WordNet) on Unix-like and Windows operating systems.