Magento Debug This is another Magento debugging toolbar based on the one for Django framework. It has similar features to the Developer Toolbar, but has a different look and feel to it. Up to developers to decide which suits them better. https://github.com/madalinoprea/magneto-debug
MageTool This tool is built to be like Zend Framework. It allows you to automate common operations, such as creating a module, controller, model, etc. It also allows for operations, such as clearing cache and re-indexing data. All of this is available from the command line. http://magetool.co.uk/
Magento PHPUnit Testing Code quality and scenarios are easy to test with this extension. Implementing a bridge between Magento specifics and PHPUnit. It allows you to find configuration problems, errors in rewrites and check if a module behaves properly with a set of incoming data. http://www.ecomdev.org/shop/php-unit-test-suite.html
Easy Template Path Hints This simple extension is useful to quickly turn on block hints by passing an additional parameter to the controller. Using it, you can avoid going to the backend and enabling the option explicitly. http://www.magepsycho.com/easy-template-path-hints.html
We hope this article will help you to get started with Magento development. Please leave a comment if you know of any useful current or future Magento developer tools or extensions.