Marketing agency owners: What system/tools do you use to organize your clients' data and tasks?

Hope you're killing your Thursday!

I was researching a bit about how marketing people/agency owners scale, and organize the work they do for their clients.

Say there are 10 clients.

And there are five to six departments/sections for each client (Accounts, Articles, Links, Ads (Campaigns), etc.)

There has to be a system or a toolset that is used to manage all of these.

How are you handling your clients' data, files, accounts, channels, and tasks?

Here is an idea: