Math Tappers apps are not intended to be stand-alone game-based learning programs – rather they are designed to support teachers and students. The apps are FREE, very simple and each with a narrow focus designed to lead to the mastery of a single concept. Personally I think their Clockmaster app is the best free app for teaching time that I have come across. I also love the way that the Find Sums and Multiples apps visualise the four operations. Furthermore, all of the apps can be adjusted to provide personalised learning.

“MathTappers: Clockmaster (Pelton, Francis Pelton, Reimer & Anderson 2010) is a game designed to help students make the connection between hours and minutes and to help them become fluent in both reading and setting time on digital and analog clocks.
MathTappers: Find Sums (Pelton, Francis Pelton, Anderson, Rail & Reimer 2010) is a simple game designed to help learners to master basic addition and subtraction facts with understanding and then to encourage them to continue playing to develop efficient strategies and eventually improve their recall speed(fluency) of basic facts and complementary numbers.
MathTappers: Multiples (Pelton, Francis Pelton, Anderson, Rail & Reimer 2010) is another simple game designed first to help learners to make sense of multiplication and division with whole numbers, and then to support them in developing fluency while maintaining accuracy.
MathTappers:Estimate Fractions (Pelton, Francis Pelton, Anderson, Rail & Reimer 2010) is designed to help learners to build their intuitive understanding of fractions by helping them to relate fractions (both symbols and pictures) to the nearest half (e.g., 0, ½ 1, 1½, 2, etc.) and then to extend their understanding bychallenging them to use fraction estimates in simple addition and subtraction problems.
MathTappers: Carbon Choices (Pelton, Longo, Francis Pelton & Smith 2010) is a personal activity monitor/calculator designed to help users (students/parents/teachers) become more aware of the amount of C02 equivalent (C02e) pollution introduced by their lifestyle choices” (p.2202).

Reference: Pelten, T & Pelton, L (2011) Design Principles for Making in Society for Information Technology & Teacher Education International Conference (SITE) 2011, Nashville, Tennessee, USA Mathematical Apps.