about: Maatkit is a package which contains high-quality command-line tools for MySQL. The tools enable power users of MySQL to do their work more safely and quickly by relying on tested software instead of scripting things themselves. The toolkit includes functionality such as table checksums, a query profiler, and a visual EXPLAIN tool, a multiprocess version of mysqldump.
about: pv - Pipe Viewer - is a terminal-based tool for monitoring the progress of data through a pipeline. It can be inserted into any normal pipeline between two processes to give a visual indication of how quickly data is passing through, how long it has taken, how near to completion it is, and an estimate of how long it will be until completion.
about: Charles is an HTTP proxy / HTTP monitor / Reverse Proxy that enables a developer to view all of the HTTP and SSL / HTTPS traffic between their machine and the Internet. This includes requests, responses and the HTTP headers (which contain the cookies and caching information).
Seems to be little more usable than wireshark!
about: GeekTool is a PrefPane (System Preferences module) for Panther or Tiger to show system logs, unix commands output, or images (i.e. from the internet) on your desktop (or even in front of all windows).
about: whatmon periodically reads a short bit of XML text from a web server (in my case: Apache). The XML contains an integer status and a single line of text. In practice, that line of text can contain whatever the administrator desires. I want an indication of the health of the mail queues on a number of mail servers we have inhouse. The line of text therefore contains two-letter codes with which I can identify the hostname of the mail server in question as well as a count of mails on the queue for each of the servers in question.