Program visualization is one of the various methods developed over the years to aid novices with their difficulties in learning to program. It consists of different graphical - often animated - and textual objects, visualizing the execution of programs. The aim of program visualization is to enhance students’ understanding of different areas of program execution. Typical program visualization techniques include code highlighting, visualization of the call stack, and presenting information on variables. Despite the large number of studies performed on program visualization, little is known about the effects of such systems on learning. We have developed a program visualization tool called ViLLE, with the main objective of offering an environment for students to study the execution of example programs - whether written by students themselves or prepared by the teacher - and explore the changes in the program state data structures. A key feature of ViLLE is language independency, including parallel execution of a program in two different languages and the ability to define new languages. ViLLE also provides role information of program variables and supports the design and use of interactive pop-up questions.