C Programs

findfiles - Find files, directories and/or "other" file system objects in a UNIX-like environment. findfiles was born of necessity. Traditional UNIX (without GNU find) had no way of searching file tree(s) for objects with names matching extended regular expressions and/or with subsecond modification/access time granularity. The things I use it most for - and I use it a lot for these - are:

Searching one or more directories (sometimes even / !) for files modified very recently. This invaluable when you need to find an error/log message, but you don't know exactly where to look.
Determining when a file was last modified to an arbitrary time (subsecond granularity). This has proved to be very useful in scripts that must determine if a file is "complete" before processing it.
Finding recently modified files of a particular name (e.g., '*.jpg') that were filed in the wrong place.

pma - A Performance Monitor Analyzer tool for Linux/UNIX.

Warning: this page contains large images (in screen real estate, not bytes) - it's not at all small-screen friendly!

fbackup - The HP-UX native backup utility (i.e., it was included with the OS at no extra cost). IMHO, HP stopped shipping it so they could extract more money from their customers by selling their other backup products. I don't have the source code, however, as that belongs to HP.
tdb - an in-memory non-relational "Text DataBase" (tdb) and reporting language that uses N-dimensional AVL trees. to approximate a sparse, N-dimensional hyper-cube. I wrote this a long time ago, but it's only very recently been released into the wild.
This program includes its own query language, which is described here: tdb Users' Guide. tdb uses a completely different paradigm, so knowledge of SQL won't help! Warning, this Users' Guide was generated by n/groff (recently unearthed by archaeologists). It's 80 characters wide, so viewing it on a small screen may prove "challenging".