Analyzing sport data becomes, every year, more interesting for a wide spectrum of researchers in the sports domain. Recently, more and more data relating to sports have become available to researchers due to the huge progress of information technologies. New wearable devices enable athletes to track performance data that are saved into sport activity datasets and later analyzed by sport trainers using data mining methods. These datasets are also very useful to researchers in the sports domain who usually employ a collection of them in their researches. Typically, these researchers are confronted with two problems: Firstly, how to gain the real data, and secondly, how to process them. In this paper, we propose a new tool for generating a collection of sport activity datasets online (named SportyDataGen), where data from various endurance sports disciplines, obtained from different mobile devices worn by amateur, as well as professional athletes are stored. The data are generated in CSV format according to user demands, and do not require any preprocessing. Here, the proposed tool is described systematically, while one example is also presented of a generated collection.