A great free app that I recommend is called Bluster!  It is a fun way to practise rhyming words, prefixes, and synonyms.  You can play single player, head-to-head, or as a team.  My grade 3/4’s enjoy playing it as a early finisher game or when I assign it as a task.

If you want more tasks, options, and levels you would have to purchase the deluxe app but for my class, I find the free app is perfect!