Double-click the DropDMG-2.8.5.dmg file to mount the DropDMG disk image. Then drag the DropDMG application to your Applications folder.
To install the dropdmg command-line tool, choose Install “dropdmg” Tool from the DropDMG menu. DropDMG will ask for an administrator password, as it needs to copy the dropdmg file to the protected /usr/bin folder.
The DropDMG service will become available the next time you log in.