Better communication within teams?

I had a client who had 10 members of staff, and dozens of tasks, messages and emails throughout the day. They were complaining that tasks and messages were not being handled appropriately and tasks were slipping through the net.
They were using shared spreadsheets to organise tasks between the team and this caused a lot of confusion.

Where can you go from here?

I advised him to sign up to a free program called Trello where you can separate all the actions into different categories, assign people to these actions and easily move actions from category to category. This way everyone can see clearly what needs to be done, by who and by when.
They have now been using this for months and recently told me that it has transformed their business.