I managed to download Fractions 1, 2, and 3 apps by Better marks. I am reviewing them as a trio because they are set up to work like volume 1, 2, and 3 of one book. The first one is labeled fraction basics, the second is order of operations of fractions and 3 is the one for adding and subtracting fractions.
Fractions 1 reviews basics such as multiplying, dividing, GCF and LCM, prime factorization. Before you start the actual learning, there is a pre-assessment for students to take so they see how much they remember. The pre-assessment covers all the topics of review. This app covers the introduction, representing fractions, converting fractions, parts of a quantity, and expanding fractions or equivalent fractions. Each section has 1 to 5 subsections. The sections provides practice problems to do. There are hints, solutions, explanations and if the student makes a mistake, the app automatically provides a hint and a chance to redo the problem. There is also a tab that states textbook so the student can read up on the material and learn to each problem. In addition, once the student has the problem completed correctly, there is a detailed explanation to read. When the student clicks on the show solution tab, it automatically shows the explanation.
Fractions 3 has a review section covering fractions, parts, mixed numbers, equivalent fractions, reducing fractions, GCF and LCM. This has the pre-assessment students can take before beginning the material. This app covers LCD, Addition and Subtraction of fractions using diagrams, addition of fractions, and subtraction of fractions.
I think these three apps plus one or two more apps would make a good unit on teaching or reviewing fractions for grades 4 on up. Just be aware there are a few terms that are a bit different than in the states but I do like the way someone can get a hint or visit the textbook to read up more on the particular aspect of fractions.