ArgentumInvoice is an open source web application for managing projects easily and billing the time worked accordingly.
It enables you to define clients, create projects and add tickets (things to be done) for that project.
The time worked for a ticket can be calculated with the help of a live timer or mentioned manually. Also, it is possible to create timesheets for every user.
At any point of the projects, ArgentumInvoice can create PDF invoices, e-mail them to clients and track invoice due dates + payment statuses.
It also supports multiple currencies and automatic currency conversions which is nice when working with multi-national clients.
The application is built with PHP & uses MySQL as the database.
Requirements: PHP 5.2.6+ & MySQL 5+