Why a cashflow app?
Cashflow often sounds like a buzz word only used by big companies. It isn't. The cashflow is the amount of money that you earn and that you spend. Your cashflow defines your liquidity. Your liquidity is what pays your rent/loan. Your liquidity is what pays your food. It is a very important thing to care about. If you are freelance, if you run a company, you've got to keep an eye on your cashflow.
Why I pay attention to my cashflow?
Ryan Carson wrote an interesting article about the importance of the cashflow a few years ago. (The Excel file linked in his article is no longer available, so I uploaded it as a Google Spreadsheet. You can download it freely by choosing File > Export > .xls)

I read this article at a time when I hadn't started my company yet. (I did 7 months after this article was published). I now really pay attention to my cashflow. It allows me to know if I've got to be anxious about the upcoming bills. It allows me to be more relax, knowing what I've got to do in the next few months.
Cashflow management tools
I've used Ryan's spreadsheet for some months. It was very handy to start paying attention to my liquidities, but I don't really enjoy using spreadsheets.
Later, I heard about Pulse, a cashflow management Webapp. They did a great job building it and blogging about their development process. I used it to manage my cashflow some times after they launched, but it is still not the best tool for me.
I've been thinking about developing my own cashflow management app for quite a long time :

I think this time has come.