Knowledge is one of the most important companies' assets, and that obtained from the experience in projects is of particular interest, as it provides the necessary tools to face and solve future problematic situations. This article presents ELLES, as a tool to generate a lessons learned repository in the domain of software development, based on the ontology LELEO, also a product of this work. The use of an ontology to attack this problem represents a great advantage, because users talk the same language both to enter the lessons learned to the repository, and for searching and browsing it, thus facilitating the generation and transmission of knowledge generated by the experiences of projects. Other features of ELLES also promoted the formation of communities of knowledge and support for new staff training. However, it is necessary an organizational schema in order to get ELLES as a daily work tool.