Although there is no app, it is possible to access RefWorks through a mobile browser: http://www.refworks.com/mobile/
Mendeley by 1) Visit the App Store or Google Play to download. Compatible with Android, iPhone, and iPad.
2) Can be used offline, then synced later
3) For more information: https://www.mendeley.com/downloads
EndNote by 1) Only available for iPad
2) Download via the App Store
3) For more information: https://endnote.com/downloads/