Rclone ("rsync for cloud storage") is a command-line program to sync files and directories to and from different cloud storage providers.
Degoo is a backup app for Windows, Mac OS X and Android that lets you back-up your data in the cloud. You also get 20 GB of free secure cloud backup storage so you'll never lose a file again.
ExpanDrive is a Network file system client for Mac OS X and Microsoft Windows that facilitates mapping of local volume to any SFTP server the user can access. It also can connect to FTP, Amazon S3, RackSpace Cloud Files, OpenStack Swift Object Storage, DreamObjects, WebDAV...
CloudMounter is a must-have tool for laptop users with low-capacity SSD-drives. You can easily mount most popular clouds as disks without having to download online files on the hard drive. As well as secure cloud files with data encryption.
Remote storage tool that lets you access your cloud files as if they're on a local disk.
MEGAcmd provides non UI access to MEGA services. It intends to offer all the functionality with your MEGA account via commands. It features synchronization , backup of local folders into your MEGA account and a webdav/streaming server.