Smith.BuildExtensions (nuget): Simple MSBuild Task that helps with maintaining app.config and web.config across multiple projects, and build configurations.  Create one app.config/web.config template and share it across multiple projects with different configurations for each build target.  Supports  * Recursive configuration transformations, i.e. one configuration variable referencing another variable * Nested configurations - i.e. one configuration inheriting from another * Project specific configuration overrides * Simple value transformations * Full element transformations
Keywords: MSBuild|App.config|Web.config|multi-project