GanttProject is a desktop software, you need a desktop environment to run it. There is no online version. However, if the question was “can you store project files in the cloud and open them from many desktops” then the answer is yes. There are many options:
- If you’re in the same LAN, you can just save files to a shared folder. In this case you save your projects on a shared folder which appears as local folder on your computer.
- If you’re on the Internet, you can share using one of the file storage providers, e.g. Dropbox, Box.com or Google Drive. Many of them allow for mounting their service to your local computer, so you again save files to “local” file system.
- In both cases you may use WebDAV server which may support file locking. It can be installed in LAN, on your own server on the web or be available as a service from file storage providers. Access to WebDAV in GanttProject is available though
Project > Web servermenu item
Finally, there are services which provide desktop environments in the browser and allow for mounting Dropbox/Google Drive folders. RollApp is an example of such service.