I've been meaning to mention my other linux operating system, Puppy Linux. It's tiny, just 150MB total. It can be booted from a flash drive and run completely in RAM if necessary, no hard drive needed. And it runs very light—I've been using it on our 12-year-old Thinkpad X24 (with just 256MB RAM). This laptop would be dead without Puppy.
And it's free, built by enthusiasts who are glad to see others enjoy their achievements. It has a very active support forum too, where I've found lots of help and tips from others who are glad to share their expertise (some of it quite extensive) and software they've written.
There are lots of varieties of Puppy Linux. I've heavily edited the one I use, so it's pretty unique. It's really been enjoyable learning about how computers operate and seeing how well I can make it run and how nice I can make it look:
These are thumbnails, click to view larger. The theme is Owl Light. And the icon set is called Faenza. These were offered free also...