Open source invoice software [UPDATE]

On a weekend, I was asked to develop a "simple" software to generate invoice, a sample document is given as reference.  First thing that comes out from my mind is to setup a template in Office Excel, that would be easy and fast.  But the idea gets turned off immediately because invoice number needs to be auto-incremented.

A simple google search leads me to Siwapp Invoice System and Simple Invoices.  I spent some time playing with the demos, here's my opinion.

Siwapp v 0.4.1
	PROS
	Easy to setup in XAMPP (Apache web server, PHP, MySQL bundle on local machine)
	Clean and pretty interface
	Built on Symphony which is similar to CodeIgniter and PHP5.3, easy for programmers to do customisations
	Able to set up recurring invoices
	Provide wiki and community forum to look for solutions
	Able to create invoice templates
	Able to add extra modules, e.g. Customers, Estimates and Products
	CONS
	Beta version, undergoing very slow development phase
	Unable to set up database in XAMPP if password field is empty unless you apply a small hack as shown here

Simple Invoice v 2011.1
	PROS
	Easy to setup in XAMPP
	Provide several types of reports
	Able to create database backup files
	Offer more configurations
	Supports PayPal and Eway Merchant
	CONS
	UI needs to be improved, should not have fix width

FusionInvoice v1.2.4 beta
	PROS
	Build on CodeIgniter PHP MVC framework.
	Simple, clean UI from Twitter bootscrap
	Ongoing development and bug fixing by the creator
	Same and more functionalities as Siwapp
	Calendar view
	Able to import .csv files, see documentation.
	Report generating
	CONS
	Cannot change invoice template from UI
	Limited search criterias
	Cannot do batch actions on invoices
	Pagination is not done in Ajax

Update:
I've done some modifications to Siwapp, check out my other post for more info.  I stopped halfway through implementing "batch invoice status update" feature.  I might continue to develop it until I'm confident to release the codes.

On the other hand, I came across FusionInvoice early today.  After playing the demo and comparing it to Siwapp, I would say it's a decent software and worth checking out the code structure.

References:

• Four Open Source Invoicing Apps Worth Checking Out
• Windows Grep: Graphical text search and replace tool for Win32 (no expiry date applied without registration)