There are 3 ways to sync your Brain between multiple computers:
Using WebBrain.com and PersonalBrain 6 - the best and safest way
Using BrainZips - also safe, but less convenient and flexible
Using a file-sync service such as Drop box - almost guaranteed to corrupt your Brain
I'm writing this post because I've noticed some questions about doing a sync of Brains through standard file-sync services. This is really not a good idea and can't be supported now or in the future - read on for the details of why. You can use a file-sync service with BrainZips, but that's it...Sync Using WebBrain.com and PersonalBrain 6
PersonalBrain 6 offers true synchronization, including the ability to add and modify information from two (or more) different computers at the same time. Links between information, file attachments, URLs, notes, images, etcetera are all synced automatically and are accessible both online and offline.
Brains synchronize though WebBrain.com exclusively because the storage mechanism is a database of complex interconnected nodes that cannot be synced without the careful analysis of metadata to support this process.
To sync your Brain using WebBrain.com, sign up online, then go to File > Synchronize Brain with WebBrain. Enter your account information and press OK. PersonalBrain 6 will automatically send just the changes made to your Brain to the WebBrain server and make your Brain available to you online.
By default, your Brain will be private to you, so that only you can see it. You can access it by logging in to WebBrain.com and looking on the My Account tab. You can now access your Brain (and soon you'll be able to make chagnes also) from just about any browser, including your iPhone.
To sync your Brain to another computer, copy it there using a BrainZip (you only have to do this once and we are working on a feature to eliminate the need for this first step also), open it and use it as usual. When you are done, use the Synchronize Brain with WebBrain command again. Any changes you made on the other computer will be downloaded and changes you made locally will be uploaded. You can even make changes from both computers at the same time. If you're busy, you can close the window that shows the sync progress and it will continue in the background... If some reason you have to shut down and can't wait for the sync to complete, that's OK too - this will be automatically detected the next time you sync.
Of course, there are lots of other benefits beyond sync that WebBrain offers and in the future, we will be leveraging the WebBrain service to make a lot of things possible that just can't be done without an online component...
Sync Using BrainZips
BrainZips are single files that contain all the information on your Brain. You can create them using the File > Create BrainZip. Once you have a BrainZip, you can copy it to another computer over a network or using a USB drive. You can even use a file-sync service to handle copying the BrainZip file back and forth for you. (This is the only safe way to use a file-sync service with your Brain.)
Each time you move from one computer to the next you should:
Obviously, you can't make changes in more than place at a time using this method, but you will avoid the possible corruption dangers.
Create a BrainZip
Copy it to the other computer
Open the BrainZip on the other computer and extract it, overwriting the last version of your Brain.
Work as usual until you need to switch computers again...
Sync Using a File-Based Sync Service
Syncing your actual .brain file and _brain folder using a file-based sync service is not possible without leading to a likely corruption of your Brain's database eventually unless you are extremely diligent in how you use it.
[The rest of this is a technical explanation of why you will almost certainly corrupt your database if you insist on using a file-based sync - skip it if you’re not interested.]
A simple file-based sync does not work properly for many reasons. For instance, many large files are modified in small but interdependent ways when the database is changed. Thus, a file-based sync is not only very inefficient, but also prone to corrupting the database. (When for example, the same database file is modified in two different places at once, a file-based sync will have no choice but to ignore one of those changes - likely corrupting the entire database!)
Additionally, there are factors beyond just the visible data that need to be kept in sync, such as index information, internal IDs that are different across machines, and so on.
This is why DropBox and other file-based sync services will work, but cannot be relied on since they tend to lead to corruption as soon as: 1) Changes are made to the data from more than one place at a time or 2) A sync is only partially completed before changes are made at the receiving computer. Worse yet, the database may only become partially corrupted so that you do not find out about the problem until weeks or months later when you cannot easily revert to a backup.
For anyone interested in this topic, do a little research into syncing independently operating databases that cannot communicate with one another on a continual basis - you will find that this is exceedingly difficult to do... WebBrain and PersonalBrain 6 sync really is a bit of "magic" - it's some of the most complex, sophisticated code I've ever seen, but it's usage is very simple.
If you're still reading, thanks for your time and attention - I hope it's been helpful.