Google announced the launch of add-ons for Google Docs and Sheets. These are third-party apps that add features to the programs.
You'll find an "add-ons" menu at the top of your screen when you have a document or spreadsheet open. From there you can browse available add-ons by going to "get add-ons". There is also an option to manage the ones you've already got. Once you install one, it will be available across all documents and spreadsheets (only in the new Google Sheets).
So far, available add-ons include: EasyBib (for automatic bibliography); Workflows (automated approvals); Avery Label Merge (address labels and name badges); Table of Contents; HelloSign (secure electronic signatures); Thesaurus; Track Changes (review and approve changes made to documents); Messenger (discuss and see changes to documents); Lucidchart (diagrams); Supermetrics (business reporting system for analytics, social media, and online marketing); Kaizena Shortcut (makes Kaizena compatible with teacher workflow automation tools); HelloFax (send and receive faxes online); Translate (use Google Translate to translate text in documents); VexTab Music Notation (add music notation, drum notation and guitar tab to documents); Gliffy (diagrams); SeamlessDocs (complete and esign documents); Charts; Ultradox Template Editor (generate, send and print personalized documents); PandaDoc (add legally binding electronic signature to Google Docs); MindMeister (turn bullet point lists into mind maps); Social Drop (connect docs to social media, keep track of retweets/favorites); Twitter Curator (find and collect tweets inside docs); Uberconference (create conference calls with all document viewers); WebSequenceDiagrams; DocumentMerge (produces multiple docs from single template); Abbreviation list (define and automatically generate table of abbreviations); Template Gallery; Merge by MailChip (send email directly from doc); iRise Requirements (load visualizations into docs); Consistency Checker (check consistency of formal docs); ProWritingAid (check for consistency, plagiarism, acronyms, cliches, redundancies, grammar mistakes, etc.); Highlighting Tools; Easy Header and Footer; and Maps for Docs.
Take a look at what some of these can do:
Google says there are "lots more" of these on the way.
Image via Google