Over offline tools there are various modern online tools that can help web developers and designers in their work, here is a list:
Browsershots it allows to test how a website looks in different browsers and different operating systems su differenti browser e sistemi operativi, effettua uno screenshot
Mockup Builder Silverlight web app that allows to create and share web sites mockups within wireframe
Adobe Kuler create color schemes
Koding online code editor with social features (actually by invite), or CodePen and jsFiddle to share/preview code snippets
Typetester allows to compare fonts rendering
Unheap is a repository of jQuery plugins and Javascripts