Even though OverGrive is a closed-source paid application, you'll want to give it a look.
At $5 per Google account, you can access all the features available on the application.But don’t let that put you off. For 14 days you can try out all the features of the app for free. After which you can purchase the full license.
Despite the name, this application doesn't rely on the now defunct Grive project. Instead it provides an easy to use GUI front end for an otherwise back end Google Drive client.
Much like its competitor InSync, Overgrive has grown in popularity among Linux users because of it's ease of use and rich feature set.
File and Folder sync directly from Google Drive
Individual folder sync
Different formats available for Google Doc files
Sync multiple licenses
There have been attempts in the past to create a reliable pen-source Google Drive sync. API limitations, a lack of active development and changing platform technologies have rendered tehse efforts fruitless thus far. If you need speed and the ability to open your files onto native apps, you're able to mount Google Drive onto Nautilus with less hassle.
While it's not a sync client, you still have many of the features of a sync client agent and more.
A comparison on its security with InSync would not be fair game, but the price rnge is an attractive difference, with InSync charging $25 flat rate compared to $5 by OverGrive.
If you've used this app, please share your experiences in the comments section below!