Jenkins and Hudson are Continuous Integration tool, commonly known as CI frameworks. They allows Java project to automate build and deployment process. By using CI tools like Hudson or Jenkins you can create hourly or daily builds automatically, you can also automatically run your unit tests and can deploy build to your QA or production environment. This helps if you are working in a large project and development team is spread across multiple locations. CI tools can trigger build whenever developer commits code and check if project is compiling or not. By the way Jenkins and Hudson are from same source tree. Hudson was original project which was open source and supported by Sun. When Oracle bought Sun, it took control over Hudson name and logistic platform of Hudson. Many open source contributors were not comfortable with that and this resulted in Jenkins, which is pretty much community driven.