Actually Microsoft's digital collaborative whiteboard might be better than trello, although both are free. The collaborative nature and the ability to attach the documents visually would make it a pretty good fit. Tons of others out there like miro.com, conceptboard.com ryeboard.com that have varying levels of "free" but I think if it's purely word docs you're working with, sticking with the Microsoft universe... Source: about 3 years ago

In our project, the change in question affected sixteen content types. Our method of documenting the content model using Mind Map diagrams in Miro meant that we could easily identify the types in question and their elements and codenames. So all we needed was a simple array of content type codenames. - Source: dev.to / about 2 years ago

In the last 24hrs I came across Mind Map, and I’m already mapping out everything that happened and every little story just waiting to be resolved. So far the service appears to be free and I really could not be happier with it. Source: about 2 years ago

Looks like miro (https://miro.com/mind-map/). Caught my eye too, looks very clean and straightforward. Source: about 3 years ago