One thing I love about the UNIX philosophy is the idea that each program should do one job and do it really well. There are zillions of small tools for UNIX-type OSes that make life much easier and are hugely useful, but they don't necessarily get written about. They certainly don't receive the same kind of coverage that Apache and Sendmail receive. One of my favorites, HTML Tidy, is a tool for HTML/Web development that I think will interest a lot of folks. HTML Tidy cleans up HTML produced by WYSIWYG editors and such.