- Collaborative online editors (revisions, comments): Google docs (revisions, comments), Hackpad, ...
- Cloud file storage: Dropbox (file revisions), Spideroak, ...
- Word processor: MS Office, LibreOffice "changes". (Yuck!)
- Content management systems: Drupal, Wordpress, ...
- Enterprise web suites: Sharepoint, Confluence, Alfresco.
- Source code control / version control: Git (and mercurial, bazaar, subversion...)
Version control is everywhere, even if you didn't notice it!