LiquidPlanner

This software helps our agency thrive and manage a lot of work with ease. We have out entire in house team as well as select contractors set up in this tool for our time tracking and project management of tasks and projects. It offers tons of flexibility and allows us to follow a hybrid waterfall/agile approach to managing work. Schedules are easy to create and export on the fly, reassigning team members and forecasting are easy, etc. It's also very easy to prioritize project work and escalate accordingly and look out and plan months in advance.

Might be a little outdated feeling in that there isn't a Trello-style board to drag and drop projects/tasks/people, though there is a similar functionality still built in to the tool. It's also not really designed to allow external project teams (your clients) into the system, but there are workarounds.

It allows for multi-platform communication between teams that are separated by distance and also time. Since project statuses are sent to email, I can respond through my email back to the software to offer updates and answers when I am away from my desk.
The drag and drop capability of including word, spreadsheeet and pdf files allows for information to be posted to the project entry allowing us to maintain project oversight at all times.

It can be complicated to new users. The interface isn't immediately clear for helping a new user understand what the product can offer. While I can respond to a email sent to me from the software, I cannot email the project directly for status updates.

Liquid Planner provides a real-to-life approach to project management. I love the way that they use a 3-point estimate for likely remaining effort for each task. This rolls up into a very useful, and dynamic estimate of project completion.

Though there are work-arounds, it is sometimes frustrating that task dependencies are tedious to enter.