PReP is a webapp owned and developed by PwC (PricewaterhouseCoopers) that aims to aid the U.S. tax partners in filing their own tax returns. It's basically a large form system that can handle complex relationships (including many-to-one and many-to-many) between fields. The PReP iOS app allows users to take a photo of tax-related items such as a W-2 or even a physical object (e.g. a couch) that was purchased by the user. These photos can then be uploaded and associated with a particular field in the form, acting as a reference for where the data in that field came from - something especially useful in the case of an audit.