ODK Collect is a replacement for paper forms with support for geo-locations, images, audio clips, video clips and barcodes, as well as numerical and textual answers. ODK Collect can evaluate complex logic to control the display prompts and to impose constraints on their responses; it also supports groups of repetitive questions and data collection in multiple languages.
ODK Collect is designed to work out of touch with a cellular network / Wi-Fi during the data collection effort. Once back in the network coverage, the completed forms can be copied out of the device or sent to a server (you control) for analysis.
ODK Aggregate is a free server. ODK Collect can use ODK Aggregate to download the form definitions and receive completed forms. ODK Aggregate can generate CSV files or publish data in Google Spreadsheets and elsewhere. There is a robust user community and many companies that can provide assistance to organizations deploying surveys based on ODK.