There is another competitor, perhaps, which is any simple, agreed-upon way to share data. For example, a Google doc and a calendar. That also has downsides, but

There is another competitor, perhaps, which is any simple, agreed-upon way to share data. For example, a Google doc and a calendar. That also has downsides, but that's probably what I would try before Trello etc. Are you trying to attract those types of people?