http://expect.nist.gov/tkbiff/
tkbiff is a mail notification program. Besides doing what it is supposed to, tkbiff is also a nice example of a polished Tcl/Tk application. It's wonderfully configurable, well documented, and also serves as a Rosetta Stone for IMAP, POP, and file-based mail servers. Tkbiff is also portable to all of UNIX, Win, and MacOS and there's a fair amount of code to make that happen just right. (The Tcl language is portable but that doesn't mean that all programs are trivially portable!)
LES: Eh, looks good. But what a totally blunt approach. It created a .tkbiff file in my home folder, but it's not just configuration. It's the entire program! Someday I'll get around to reading all that and making it work. :-(
DL: I'm not sure 'blunt' is the right word to describe it but it certainly doesn't follow the traditional approach of making everything a pre-defined Preference. Instead, the entire GUI is there in your .tkbiff file! This reason for taking this approach is explained in Q1 of the FAQ: http://expect.nist.gov/tkbiff/FAQ.html#q1
While deciding if you agree, I ask you to think about your present email checker and ask yourself - Is there anything about it you'd like it would do differently but are unable to because there is no Preference to change it?