Testception is a tool that generates interactive exercises for teaching software testing to introductory students. Students submit test cases to the system, which uses a large corpus of buggy programs to evaluate these test cases. Students then receive automatic feedback in the form of of buggy programs that their tests failed to catch, enabling them to reason about the deficiencies in their test suite. Testception is described in detail in our paper, and you can find its source code at https://github.com/rice-cs-edutools/testception.
MemStep is a web-based tool designed to teach students about the run-time layout of memory in Java, described in detail in our forthcoming paper "MemStep: An Interactive Tool for Constructing and Visualizing the Run-Time Memory Layout of Java Programs". You can access MemStep at https://tools.owltest.org/memstep.