Jira may be extremely sluggish and require a large amount of memory on the client side.
Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
Modelio - Modelio is an open source modeling tool supporting natively UML, BPMN and model exchange with XMI.
Asana - Asana project management is an effort to re-imagine how we work together, through modern productivity software. Fast and versatile, Asana helps individuals and groups get more done.
Diagramo - Diagramo is an online flowchart software - diagrams (create, edit and share)
Wrike - Wrike is a flexible, scalable, and easy-to-use collaborative work management software that helps high-performance teams organize and accomplish their work. Try it now.
UML Designer - UML Designer provides a set of common diagrams to work with UML 2.5 models.