In addition to redundant copies on USB drives stored at different locations, I suggest burning the entire source tree to CD/DVD and placing it in a safe deposit box with a bank. Of course, you'd need to 'refresh' that on a regular basis.<p>In some situations that is an acceptable solution to escrow requriements too. But you'd need to consult a lawyer on that.<p>IMHO any cloud solution is not secure enough for truly valuable software. Of course, you could encrypt and use more than one service - e.g. DropBox and iCloud and GoogleDrive. But ...