First, i want to make a distinction between the two process, and clarify some terms: The Sale process and the Invoicing process (and also the Delivery process).
The sale process in general, follows the following steps (I can use the Term stage in place of Step, but as this term has a specific meaning in OpenERP, i'll use the term Step): Lead --> Opportunity --> Quotation --> Sale Order. But those steps are not mandatory, and we can begin the sale process at anyone of the above Steps.
The Sale Order, passes through the following Stages: Draft Quotation --> Quotation Send (To customer) --> Sales Order (Received from customer = Quotation received and approved by customer) --> Done (Sale operation executed, and trigger Two new processes: Invoicing (in Accounting) and Delivery (in Warehouse)).
The Invoicing process, begins when the Sale Order reaches the stage "Done". And it passes through the stages Draft --> Open --> Paid.
In the invoicing process stands the Proforma Invoice, which can be considered just as an intermediate stage between Draft and Open Stages, to be sure that all is going well.
A definition from WIKIPEDIA:
<< Simply, a "pro forma invoice" is a "confirmed purchase order" where buyer and supplier agree on detail and cost of the product to be shipped to the buyer. A pro forma invoice is generally raised when the seller is ready for dispatching the material but he wants to ensure that the payment is being sent before dispatch.>>.
In the actual worflow (sale.basic.workflow), the Invoicing process is considered as a Subflow.
About "The workflow in Sage":
In OpenERP the above processes remains independent, and you can begin by the Invoicing process first, without the need of a Sale Order.
In OpenERP, you can even change the existing workflow.
About "Question: Is there a way to emulate the Sage workflow in OpenERP, so that":
1_ Yes, you can print and send the Proforma to the customer (we can add also a "SEND TO CUSTOMER" Button.
2_ Yes, (some modules) can give you the ability to cancel it, and reopen it in a Draft State ...
3_ Yes, payment can be made against proforma, and even without proforma, you have later to reconcile payments
For INDE TRUCK SL: (AFAIK, Proforma Invoice is not a mandatory step with all customers)
OpenERP gives you the ability to:
- Generate Invoice based on Sales Order Lines Or after and based on delivery Orders
- Allow Proforma Invoices (or not)