A Basecamp developer primarily works on the Basecamp project management software, enhancing its functionality and fixing bugs. They design, code, and modify the software, tailoring it to user needs. They are involved in every stage of the software development life cycle, from planning to testing. They work with different programming languages, including Ruby on Rails, and collaborate with other team members to develop new features. They also ensure the software's security, performance, and stability. Additionally, they might communicate with customers to understand their requirements and troubleshoot any issues they face.