Though we're only highlighting the most widely adopted and feature rich solutions here, we'd encourage you to check out Wikipedia's rather comprehensive feature chart
comparing dozens upon dozens of different remote desktop products if you'd like to dig deeper into the matter.
And this doesn't mean take a look at two or three potential competitors, but really delving into your particular topic / subject niche and
comparing the pricing points of
dozens upon dozens — if not hundreds — of different e-book prices.