SPSync is a very powerful tool, sitting in the taskbar and works like Dropbox. It automatically sync folders you choose with document libraries in SharePoint 2010 and SharePoint 2013 (including Office 365 / SharePoint Online). It provides a full two-way sync mechanism.
CAML Query Creator is a set of tools for fast and easy creation of texts CAML- queries via the lambda expression.
SPCascade lets you create multi-level cascaded dropdown lists on a SharePoint form using easy JQuery code.