Thanks for the feedback on Flitestar, maehhh - you are the first real user I have made contact with, and I am grateful for your opinion.
Dark Helmet has pointed me (above) to a free, web-based version of Sky Demon, which I have looked at briefly and which seems quite interesting, especially for a free product (obviously, they hope you will pay to upgrade to the full version, which is in the same price bracket as Flitestar).
If you have time and are interested, do take a look at it, perhaps it will do all you need. It's certainly simple, and apparently doesn't need annual updates.