tomos wrote
I work on my own, selfemployed, but very few clients
That is exactly what I do. I have an agenda where I enter the work I do (start, duration or end) project. If you get paid by the hour, then billing is easy. The pivot table (or select durations and right-click>info) will give you the hours to bill.
You could have a grid for each bill and use the HTML Export>Template to automatically generate nice looking bills. Set the billing no. to those items (select all items and change the billing no. in the properties pane to batch change values) and hop, they disappear to show only tasks that haven't been billed.
I also enter all project notes in a tree structure. If tasks or sub-tasks require followup, I click the followup checkbox (grid or form). Another grid gives me all items that require followup (with or without context parents)
You could also use it to gather web clippings using the HTML pane or link it to web pages (select company A, web page opens automatically, or select your bank account item, etc.
Notice the ToDo grid. It has a very complicated filter to show just those items requiring attention (items automatically get color coded based on the Urgency field which is calculated from DueDate, Duration and %Done)