Today's Emacs Lisp package tidy-up is of a package I first wrote a couple of employers ago. While working on code I often found myself viewing FASTA files in an Emacs buffer and so I thought it would be fun to use this as a reason to knock up a simple mode for highlighting them.
fasta.el was the result.

While I doubt it was or is of much use to others, it helped me better understand simple font-locking in Emacs Lisp, and also made some buffers look a little less boring when I was messing with test data.
As for this update: it's the usual stuff of cleaning up deprecated uses of setf, mostly.
If bioinformatics-related Emacs Lisp code written by a non-bioinformatician is your thing, you might also find 2bit.el of interest too. Much like fasta.el it too probably doesn't have a practical use, but it sure was fun to write and taught me a few things along the way; it also sort of goes hand-in-hand with fasta.el too.