I've uploaded a free script to my website and you're welcome to download it.
This little script is a great. It simply cycles through three of InDesign’s capitlization options: All caps, lowercase, sentence case.
Although InDesign lets you assign a separate shortcut to each of the options, I find that I miss the possibility of cycling through the options and I find it annoying that you have to select the entire word to change its case. This script takes care of that, and provide the equivalent functionality of the Shift-F3 function in Microsoft Word.
With this script you can simply place your cursor in or near a word, or select some words or letters, and hit the shortcut key you’ve assigned to the script. One press will turn the word from lowercase to Sentence case. Another press will turn it into TITLECASE. And another press and you’ll be back with lowercase.