The DropBox client is done as a plugin for NetDrive. So as a requirement you need NetDrive.
NetDrive for OS/2 is a virtual file system which allows to create a virtual volume and mount various resources to the volume. Current version of NetDrive for OS/2 supports local, network and FTP resources. More Information about NetDrive can be found at the developers home.
PMView Pro: a versatile and fast image viewer and converter. It supports over 40 graphic formats (gif, jpg, jpeg, bmp, tiff), converts to and from them, creates thumbnails, and more.
DFSee is the SWISS-ARMY-KNIFE for disk and filesystem problems. It has FDISK-like displays, cloning, imaging, analysis and recovery tools with powerfull FIX commands and UNDELETE for HPFS and NTFS.
Qt makes software development smarter. It is a powerful plattform neutral framework that makes it easy to bring many applications to OS/2 that were written for various other plattforms.