At the time of this writing there are two ways to approach this, each with its own drawbacks.
- No matter what type of Trello account you have, you can create multiple "Teams" and give different Boards to those teams. Teams, in many parts of the UI, give the same effect as folders. For instance, in the dropdown Boards list, you can collapse lists of Boards by Team. So, if you're an individual, you could make a number of "Teams" with names like "Work," "Home Projects," "Templates," "Fun Stuff" or whatever, and your Boards would be grouped that way. The caveat here is that if you're interested in upgrading to Business Class for all the additional functionality, you can only do this with one Team, unless you want to pay for a subscription for each one of your "folders" (and unless you have unlimited money, this would be insane). Here's an example of this in action:
- If you are a Business Class user, then chances are you can't use option #1. However, Business Class comes with a feature called Collections. Collections are essentially a way to tag Boards. You can view Boards by Collection on the Boards page, but the drawback here is that you don't get the same collapsing feature on the Boards dropdown that you do when creating "Teams" as a folder hack. You can still use option #1 to simulate folders, but you'll have to forego having any Business Class features on the Boards you assign to "Teams" that aren't your Business Class Team. One upshot here is that you can add a Board to more than one Collection.
The only way to get the best of both worlds, as of this writing, is to make a team for each "folder" and buy Business Class for each of those teams. This is prohibitively expensive for the vast majority. I do hope Trello implements a folder feature on the Boards list at some point.