Albert.io provides many free and premium options for AP exams. The free version of Albert helps the students to try many quizzes for free, whereas the premium students can access dozens of quizzes. Some of the AP prep includes free-response practice questions.
Anki USP lies in seamless connectivity and synchronization with AnkiWeb, a free online server. This allows users to retain decks synchronized across multiple computers, and to study online or on a cell phone. Comprehensive support gives credible information for users to track their statistics on different aspects of performance. Anki study tools pricing model is also a high selling point.
Desmos USP lies in its amazing calculation abilities and ease of use for all professions. Desmos is used by millions of students and teachers in nearly every country in the world and has been translated into 30 languages. Affordable Desmos pricing policy also makes it more attractive for all.
Kahoot! USP lies in multiple connectivities and sharing ability through apps, such as Google Hangouts, Skype, and more. A generated game PIN helps users to connect on the common screen, after which the players through their personal devices can answer questions created by their masters.