We present UCCAApp, an open-source, flexible web-application for syntactic and semantic phrase-based annotation in general, and for UCCA annotation in particular.UCCAApp supports a variety of formal properties that have proven useful for syntactic and semantic representation, such as discontiguous phrases, multiple parents and empty elements, making it useful to a variety of other annotation schemes with similar formal properties.UCCAApp's user interface is intuitive and user friendly, so as to support annotation by users with no background in linguistics or formal representation.Indeed, a pilot version of the application has been successfully used in the compilation of the UCCA Wikipedia treebank by annotators with no previous linguistic training.The application and all accompanying resources are released as open source under the GNU public license, and are available online along with a live demo. 1