Wordle was fun to play with; at first I didn't use enough text, but I can see how kids and teachers would thoroughly enjoy using it. What an attention grabber it could be at the beginning of a lesson. Voki was fun, except that it told me my password was wrong when I tried to sign in again. Bookr was a blast. I can see how students would really enjoy using Bookr as an alternative to standard written assignments. It would also be a great way to do a lab write up in a science class. Of course, kids would love Voki - it's almost like a quick little "tweet" that could be attached to email and changed on a daily basis.
Here's a Wordle example for summer.