Open source is a way of working that goes beyond traditional software production. The number of non-developer users of open-source software (OSS) is growing, which has led to an increase in decentralized OSS production. OSS communities do not know how to apply usability techniques in the development process. The goal of our research is to incorporate the usability technique Organization of help by Use Case (OACU) into the OSS Sleek project. For this purpose, we participate as volunteers and have the authorization of the developer of the Sleek project. We used the case study research method during the application of the technique and solicited the participation of the OSS community. The biggest challenge in applying this technique was to involve expert users. To this end, external users with intermediate-advanced knowledge in projects similar to Sleek were recruited through e-mail dissemination. As a result, we identified the adverse conditions that complicated the application of the technique and modified them for application in OSS projects. We can conclude that the results obtained were favorable as the modifications made helped to apply the OACU technique.