WhiteRabbit allows you to create tasks, customers and taxes and affects them to na unlimited number of projects independently to your subscription level.
Define projects for your customers. Create tasks with different prices and link then to your projects.
Define your hourly rate according to each task and link them to a tax rate for invoicing purposes.
Tasks are the main billable elements within a project. You can define as many tasks as required and attribute them transversaly to different projects.