As an open source developer you may be eligible for special offers. This post lists some of them.
Visual Studio development
For ReSharper, a Visual Studio plugin, you can apply for a 1 year Open Source License. For debugging, watch OzCode‘s offer. CppDepend, an architecture analysis tool, is available to projects that use C/C++ as the programming language. PVS Studio can do static code analysis.
For Java UI components, JIDE makes an offer. Excelsior JET converts your Java code into an executable. IntelliJ offers a 1 year license. JArchitect helps you keep the architecture right. Gluon, a Java cross platform development framework, happily provides 1-year licenses as well. You can also get Chronon, which monitors your Java performance.
Others / programming language independent
Open source projects may use Atlassian products (you have heard of JIRA) for free. Xamarin, a mobile platform framework, wants to help open source developers. If you need a cross platform installer, InstallBuilder might be your choice for the open source project. Doesn’t fit? Maybe Advanced Installer does if you’re on Windows only. Mockups might be created with the free license of Balsamiq. If you’re keen on Python and the Pycharms IDE does not suit you, Wing IDE works on Linux and iOS. Perhaps Aquafold database is also helpful. Like IntelliJ and Resharper, PHPStorm is also available.