Do you often find yourself hitting CAPS LOCK without noticing, meaning you have to retype your sentence? Forget whether the number pad is on or not? Are you that rare breed of person who uses Scroll Lock?
If the answer to any of these questions is 'yes' then NumCapsScroll Indicator will be useful. After a quick installation, you will see both a neat three-bar indicator in the System Tray, and a small floating movable panel with Num, Caps and Scroll lock indicators. Tap Caps Lock, for example, and the indicator will light up, and make a click sound. The visual and audible (which can be silenced) signals make it hard to miss if any of the keys have been activated.
For people who type a lot, this is actually a cool tool. Having indicators on-screen is much more sensible than on the keyboard. In terms of functions there is little more you could ask for, although the scroll lock indicator is more or less redundant (like the key itself). An Insert status indicator would be a good addition. However, if you're writing an article or an essay, the 'always on top' floating NumCapsScroll Indicator panel is certainly useful.
This is certainly a niche app, but could be especially helpful for touch-typers.