I'm sorry, but these products — thousands, and all gugliada. Many programmers like to start your career path with these services, so they are presented in a huge range. Especially "simple" and "loose".
Gantt chart — so basic thing that is present almost everywhere. In the repositories of Linux has a dozen planners, some of them group. Planner with a Gantt chart is even in the email client!
Many of the programs available for other operating systems, such as planner, evolution and others. With web interfaces, a dozen projects were announced, including on habré. There are many in github, and with good reviews (including those named above).