Basecamp

Basecamp is online project management software. People can create, manage and communicate tasks, files and to-do lists.

Basecamp is developed by 37signals and launched in February 2004. 37signals started designing websites in 1999 and created for each project a private network to simplify the communication between the company and clients. Soon they started to develop a web based service which could create such an extranet quick and easy on the fly. After 37signals realized such an application would be helpful to a lot of organisations Basecamp was born.
Basecamp is an online tool to create and manage projects. A project includes To-Dos, Messages, Files, Milestones, and People. New project are created within minutes. People working on a project automatically get an email notification when a new post is added to a project. Instead of emailing each other for every task all information is well documented in one place.

Basecamp is not the most extended project management tools but it is one of the easiest to use. Which is important because you're clients might be first-time users.

With the free version of Basecamp only one project can be active and there is no storage for shared documents available. If SSL security, time tracking and more writeboads, storage space and active projects are needed you need to buy a business plan ranging from $12/month up to $149/month: Basecamp business plans.

http://www.basecamphq.com/