WingFS lets you connect to Amazon S3, Google Cloud Storage, DreamObjects, EMC Atmos, Generic S3, Google Drive, OneDrive, Dropbox, box, Rackspace, HP Helion, OpenStack, WebDAV, FTP and SFTP. More cloud services might be added later.
Download the software and double click on the installer. WingFS as well as OS X Fuse will be installed on your Mac. Once the installation is completed, you can connect to your different cloud services. More information here.