Parabol is an online tool that can be used for conducting agile team workshops aka Retrospectives online. It is primarily used by virtual or remote teams, who often work (according to the Scrum Framework) in sprints and prefer to use varying retro templates at the end of their iteration. Parabol is open source and offers and on premise solution.
On the other hand, TeamRetro, Parabol’s alternative, is a cloud based retrospective tool with a stronger focus on ease of use in running effective retrospectives, more features on creating actions and has the ability to create surveys for health checks and team agreements. It has useful and relevant reports and Insights that allow teams to continuously improve.