Cloudflare Apps allows you to install a wide selection of apps onto your sites. Many of these apps are free and you can use them on all your sites without paying a dime! You may use Cloudflare Apps and those apps on it which are free for as long as you like, free of charge.
Those apps which are paid are clearly marked along with their price, which is billed monthly. Most paid and free apps alike offer a Live Preview to allow you to see how the app would perform on your site before installing.