Investors have long assumed that Rosetta Stone (RST) had a lock on the business of software-driven language learning. Many still do: The stock is up more than 44% over the past year.

Is that fair? We'll find out more when the company reports fourth-quarter earnings this week. Revenue is expected to be up slightly, resulting in $0.09 of profit versus last year's $0.24 a share loss.

In the meantime, some Fools point to a disruptive new service called Duolingo, which claims to teach languages even more efficiently than Rosetta Stone does. There aren't nearly as many languages in Duolingo's library, of course, but it's also free to use. Rosetta Stone, meanwhile, pitches its strong relationships with educators as an advantage.

Tim Beyers, of Motley Fool Rule Breakers and Motley Fool Supernova, has tried both services, and weighs in on the threat to Rosetta Stone in the video below. Please watch, and then be sure to leave a comment to let us know what you think.