Hi there,

There are quite a few options:

• You could upload files directly via the DigitalOcean Control Panel
• You could use the s3cmd command-line tool
• If you need to upload files via your web application, you could use a specific library depending on the language that you are using
• Another option is to use OwnCloud if you are planning to use the spaces for storing static files
• If you are specifically looking for a Cyberduck Alternative, you could try out FileZilla for example or take a look at those alternatives here as well.

It really depends on your requirements.
Regards,
Bobby