If you would like to export one or more items, you can do so in the following formats. These formats allow you to migrate your items from one tool to another (note that these formats do not include file attachments).
Note that to export from EndNote to Zotero, you can Export citations from EndNote using the .xml format, and then Import them with Zotero.
EndNote: highlight references you want to export, can export to .txt, .rtf, .htm, .xml formats via File menu
Mendeley: highlight references you want to export, can export to .bib, .ris, .xml formats via File menu
Zotero: highlight references you wish to export, can export to BibTeX, CSV, EndNote, Refworks, MODS, and more formats by right clicking