One of the subjects with the most potential for online education is language learning. With so much audio and video in every conceivable language on the internet, teachers have to rely much less on rote memorization, textbooks, and traditional lecture-based classes. 

One innovation that is particularly relevant to the concept of ubiquitous learning is the language immersion plugin (there are several variations available on the Chrome web store), which I first saw described here. 

Although the features vary, all of these extensions allow you to specify a language and an immersion level. Then, as you browse the web normally, the extension will use Google Translate to randomly replace a certain percentage of words (based on your reported immersion/fluency level) with the equivalent word in your target language. By hovering your mouse over the replaced words, you can see the original text; some extensions also allow you to click on the text to hear it read by a native speaker.

For a language teacher, this kind of program can be used to extend the learning space not only beyond the typical physical classroom, but also into the students' normal daily lives. As they read, shop, or play games online, they will automatically be exposed to new words in the language they are studying. Since most of the page is still in the original language, context clues can be used to determine the meaning of unfamiliar words.

These extensions have some problems, most obviously their reliance on the still-far-from-perfect Google Translate service. The words chosen by the extension are often only awkwardly translated (I tried it with Chinese, and it replaced 'pronounced' – as in pronunciation – with the Chinese word for 'pronounced' as in emphasized or very noticable). Also, since these extensions were written for independent language users to install on their personal web browsers, there are currently no options for teachers to access data about what their students viewed. It would be helpful if teachers could supply vocabulary to the extension, so that only words covered so far in the normal course program would be replaced.

Still, combined with a more regulated curriculum and more structured learning, these tools enable teachers to take the "anytime, anywhere" aspect of online learning and extend it to students' lives in a way that normal online study tools would fine hard to match.