xmobar is a text-based status bar originally designed and implemented (in Haskell) by Andrea Rossato. In December 2010, i accepted Andrea's kind offer to become xmobar's maintainer, after having contributed a bunch of patches.
Lightweight status monitors have always been a must-have in my desktop, and over the years i've used many of them (xload in the olden days, gkrellm, conky…), so i guess it was only natural that i ended up maintaining one. That xmobar is written in Haskell is a big plus in my book.
I'm the author of GNU MDK, which stands for GNU MIX Development Kit. It is an emulator of Don Knuth's MIX mythical computer, together with a MIXAL (MIX Assembly Language) compiler that produces assembly object files executable by the companion MIX virtual machine. It also allows debugging programs through step by step execution, breakpoint setting, symbol table inspection and manipulation of the contents of MIX's components (registers, memory cells and the like).
All of this can be done via a comfortable command line interface or, if you really are that kind of gal or guy, a gtk+ GUI. Last but not least, the whole enchilada is controllable, extensible and what not using the most beautiful programming language ever.
Over the years, i must have tried every single window manager out there. Before finally settling to exwm, i kept returning to one of my first loves, sawfish, and have a soft spot for xmonad. My sawflibs project contains a couple of libraries for sawfish: the most significant of them (sawflibs.tile), grown out of xmonad envy, was incorporated into sawfish proper in version 1.10.
Factor is an amazing language in the concatenative family. There're many things i like about it, but probably the one i find most enjoyable is its fully reflective environment, which in many ways evokes the Lisp Machines of yore. Given that, it was not too difficult to implement a nice Emacs interaction suite for Factor, which we called FUEL. It comes bundled with Factor itself, and you can see it in action in this nice screencast by Slava Pestov.