For what I have searched, Voki is a character that can be customized according to the students´ preferences. As the website provides the information (you can have access by clicking the previous link) in a clear and easy way, it is really simple to create your own Voki. They can be used to engage students´ attention and to make English lessons not that monotonous by making students participate more actively. It is not only useful for students but for teachers as well. Teachers have a whole section called "Voki classroom" (unfortunately you have to pay for it), where they can check their students´ improvement and homework, a kind of Edmodo Platform. But if you cannot pay for it, you can create Vokis anyway and share in different websites such as Facebook, Blogger, Google, etc.
Wordcloud, on the other hand, is not a character but a tipography tool instead. You can create one by counting words in some text. This could be a Microsoft document, a pdf one or you can introduce the words by tiping or pasting a text. It is a really interesting way to grab students´attention by using something new to teach vocabulary, for instance, and not the typical pictures posted on the wall. The one I chose is free and easy to use.
Source:
Voki
WordCloud