Zotero

Zotero's sync feature is an excellent way to create a backup for your research. It also enables you to work on your research at multiple computers. Zotero can store a copy of your library on the Zotero.org server and check it for updates whenever you open your library on a different computer. All your computers must be running the same version of Zotero.

First, set up a (free, of course) Zotero.org user account.

Then: 

1. Open Zotero preferences (via the Edit drop down menu) and select the Sync tab.
2. Enter your Zotero user name and password.
3. Check the "sync automatically" and "Sync full-text content" boxes.
4. Check both boxes under File Syncing and choose Zotero storage for My Library. This will sync your PDF attachments as well as citations (more info).
5. Click the green circular arrow button at the top right corner of the Zotero library.
6. Zotero will upload your library to the server.

Repeat this configuration on each of your computers. Any updates you make on one of your computers will be reflected on the others. This process even works to synchronize your library among Windows, Mac, and Linux computers. 

If you're working on a library computer, there's another easy option for taking your Zotero library with you.

Within the Zotero application, select Export Library from the drop down menu, choose format and select whether you want the notes and/or the files exported, and save the file to your USB drive. On the new computer, open your Zotero application, select Import from the drop down menu and find your Zotero file to import your references.

Gif example of how to export to a flash drive:

When you're done, make sure to export any changes and import the new file onto your computer. The library's computers will erase your data when you log off.