Lots of cash book applications around. None work on Drupal, making them difficult when you already have all your contact information in Drupal. I propose a simple cash book/day journal module for Drupal with an API to help hook in with Storm, CiviCRM, and other modules containing contact information.
There would be a base Cash module then there could be optional cash_storm etc as required to connect to existing contact information. Accounts, customers, and other item types would each have a node type so you can type notes into the body of an item. The module would work out of the box with core Drupal 6. Connections to other modules would depend on the facilities provided by the other modules.
One output would be a file to pass to accountants for input to their accounting systems. Probably a CSV file.
The project would start with a single currency. I have a need to add other currencies with conversions recorded as actual amounts, not calculated amounts. That is one of the problems with some accounting systems, they perform an almost always wrong conversion when the foreign currency hits an account then you have to apply an adjustment after the actual converted amount shows up in your account. I would enter foreign amounts with a flag indicating they need conversion. When comparing transactions to account statements, you then enter the actual amount with the foreign amount remaining as a note.
I require part payments for invoices, something that is painful in a lot of cash books.
I require quotes in the system somewhere so they can convert to invoices with the conversion allowing for addition and deletion of line items. Although production of quotes and invoices are not part of the cash system, saving retyping of quotes as invoices and line items as transactions will be a big data entry saving if it is done the right way. Optional modules could connect to Storm, Ubercart, and other applications to find invoices with their line items when entering transactions.
The system will eventually have to allow for multiple businesses and multiple accounts for each business and accounts shared between businesses. Several contractors could then share a credit card or a cheque book and have separate reports for their own transactions.
I like the way Storm handles project items but the invoices lack a lot of the features I require. Ubercart should handle everything I need in invoicing. I can see how Cash could take time items from Storm, create line items for payment, send them to Ubercart for a nice Invoice, get back the invoice identifier from Ubercart then create invoice/line item pending items. When the payments arrive in the accounts, you could just tick them as paid and get the cash journal automatically. The unpaid items would sit there as a reminder.
A lot of small items are often included in one payment. There is a need to connect items owing to payments and show the difference until you connect all the items included in the payment. This is to help you match payments when you get your account statement.
There is a need to mark items as done when you look at your online banking details then to mark them against printed statements because printed statements do not always match up to online displays by moth or day or anything else.
There is a need to mark items as sent to the accountant so missing items can be entered at a later date and sent. Many accounting systems have an insane system of locking up accounts by month. You have to then enter everything as adjustments and that is many times more work. If we can enter items when they are created then mark them off when they are paid, we can see the missing items and chase them down before they become nasty prior period adjustments.
Cash would be stacked as a set of modules so you use only what you need.

Comments
ERP module...?
Have you checked out the ERP module (http://drupal.org/project/erp)?
Will look at it
Hello arpieb, Thank you for the suggestion. I will look at it. The quote to invoice part could be useful.
I try to keep away from projects that depend on non core modules. With several of my sites already on D7 rc3, the list has expanded to the extra modules in D7.
There are several PHP based ERP projects with cashbook components that are almost unusable because you cannot switch off what you do not use. I will look at the flexibility of the ERP module.
The timesheets module could be useful. I hope they share development with Storm including the Storm time recorder.
petermoulding.com/web_architect