Zotero PDF Translate automatically translates PDF files, annotations, notes and item titles. It uses Google Translate (by default) and other automatic translation tools.
A plugin that makes your Zotero "look great": it modifies some of Zotero's existing columns and adds some new ones.
Zotero Abstract Cleaner allows you to fix line endings in abstracts in Zotero.
Zotero is open-source, and it is easy for anyone to create additional tools to add functionality to the program. Over the years, many plugins have been created that give users the ability to customise Zotero to their needs and preferences.
To install them, the usual procedure is to download the file (with an xpi. extension) to your computer, then go to the Tools -> Plugins, click on the gear on the right, select Install Plugin from File and select the file.
For a complete list of Zotero plugins, click here.
Zotero Actions & Tags is a plugin for managing tags, with batch processing and the ability to set custom rules.
This plugin can auto-fetch DOIs for new items, shorten DOIs using http://shortdoi.org, and check the validity of DOIs.
A plugin to format item metadata and check for duplicate items when new items are added. It adds shortcuts and a pop-up toolbar to bold or italicise words, automatically adds or corrects the abbreviated title of a journal, automatically corrects certain errors (e.g. importing a document with the item type "web page" and a URL containing the name of a major academic publisher may be an error), automatically adds some missing information.
Zotero Attanger and ZotMoov are plugins that help you manage your attachment files. It allows you to automatically move your attached files to the directory of your choice, inside or outside of Zotero. Both can allow you to store your PDFs on an external server when you reach the limit of the free storage space on the Zotero website.
A sophisticated plugin that can make Zotero a great note manager. Lots of features, but a manual is included.
More details here.
This plugin adds the ability to perform an OCR (optical character recognition) on PDFs selected in Zotero. It can add a new PDF with the recognized text, a note with only the recognized text, and HTML (HOCR) files.