A free program for Android, by Nicholas Howe.

This app lets you create the funniest audio reaction videos ever. Just record your voice and upload it to the app. It can be used in any application, including video games, movies, and more. It’s a lot of fun to create reaction clips and it’s even more fun to listen to them! It’s all done in a clean and easy-to-use interface, so even if you have never made an audio clip before, you can do it in a few minutes.

Comedy FX Soundboard is the best app for audio reactions and will help you become a comedy star.