Mentimeter is a great tool that you can use in the classroom to do engaging activities with your students. You can create multiple choice or open-ended questions, or word clouds that you can show on your computer or television screen and that your students can answer using their phones. I find it specially useful for creating activation tasks, for example:

You may create an activity centered around a short video about life in the future that students will watch. As an activation task, you may create a Mentimeter wordcloud with the question "How do you imagine the future world will be?" and ask students to answer it. Then, you can easily see the most common answers based on the size of the words in the word cloud. This way you can activate prior knowledge related to the topic or even use those answers as a while-watching activity, checking if those words are mentioned in the video.

Kahoot is a tool for creating interactive quizzes that you can host in your computer and students can join from their devices using a code. In my experience, it is extremely easy to use and it can gamify regular activities adding game mechanics like points, scoring and countdowns in competitive or cooperative quizzes.

For example, you can create a reading comprehension activity with a Kahoot quiz after completing a reading activity about endangered species. In it, students join one of two teams in the game lobby and then answer multiple choice questions related to the reading activity (for example, "What endangered species are mentioned in the text?"). The faster they answer correctly, the more points they get, and those points are added to their teams total score. Therefore, you can create a gamified activity that possesses both cooperative and competitive aspects.