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!