You don't need an app for full and integrated Google Drive and/or Dropbox support on Windows Phone.
In complete disbelief you might utter words like:
We wish we were the ones to make an app for that, just like we have done for Gmail. For for Dropbox, it is much much easier, and perfecly integrated. All you have to is sign up for cloudHQ and syncronize the files between Skydrive / OneDrive and Dropbox
But, hey - isn't that crazy difficult?
No, not at all - see below
First of all you need to be a member of all the services
We assume you are signed up for all three accounts, and logged on to cloudHQ
Click syncronize at the top of the page to get into the Syncronize settings. This is were it all begins.
Drag the icons of the services you want to sync to the boxes at the top, so go do it, drag Google Drive to the first box.
Here you should select the area of Dropbox you want available on your Windows Phone (remember this also needs to fit on your Skydrive / OneDrive account) so if you have more than the size of your Skydrive / OneDrive account you need to be selective - I am going for the lot here.
Likewise choose the area of your Skydrive / OneDrive account that will be available on Dropbox, I am choosing a subfolder (Documents), but I also have A LOT of pictures on my Skydrive / OneDrive.
Here you can choose your sync settings, since we want files to be the same on Skydrive / OneDrive and Dropbox, we choose Syncronize Continuously.
Get a cloudHQ account and sync Skydrive / OneDrive with Dropbox for full use of Dropbox on Windows Phone.
The lowdown: Get a cloudHQ account and sync Skydrive / OneDrive with Dropbox for full use of Dropbox on Windows Phone.
For your Gmail needs, we have a really nice app for Windows Phone
Find your new Windows Phone at the Microsoft Store: