What is Trello?
Trello is probably a project management tool that most people have heard of. It was one of the first project managers to hit mainstream popularity because it was the first project manager to allow for kanban board view from a web app, bringing with it a super user friendly interface.
This was an incredible feat back in 2011 and what resulted in its rise to popularity, especially in the B2C space (general consumers, not majorly breaking into the B2B space). For example, you'd use Trello to manage your personal tasks, maybe more as a prosumer, and less as a business owner.
We used Trello here at Efficient App for years, before ultimately switching to Asana, when they too added kanban functionality, as we felt that Trello sort of got a bit stuck, while their competitors were evolving and working to further innovate in the project management space.
Key Features
The main differentiation that Trello had was kanban board functionality, and that's about where it started and ends. Thing is, kanban view is now a staple of any modern project manager on the market in this day and age.
Feature set wise, since Atlassian now owns Trello, they've prioritized integrations within the Atlassian suite.
User Experience
Trello does board view well, but that's about the bulk of it. As they haven't really seemed to update Trello much in the past 6+ years, the bulk of the credit that we can give Trello comes from it having incredibly deep integration with the Atlassian suite of tools (e.g. Jira,Confluence, and Bitbucket).
With Atlassian's acquisition of Trello, came with it more of an integration with Atlassian's tooling.
Mobile App
Trello actually has a pretty solid mobile app on both iOS and Android. This is in part to how much time they've had to perfect it. Early on, being more in the B2C space, and coming out more when the iPhone was gaining major traction, a solid mobile app is something that the general consumer wanted. So this is something they've spent a lot of time perfecting.
API & Integration
We also have to give Trello credit in this area. They have a super robust API and powerful Zapier connector. If their Zapier connector doesn't have quite what you're looking for, you should be able to do chat you'd like to do using their developer API.
If your team is heavily relying on the Atlassian software stack, then Trello is likely to bring with it some native integrations to help your team out as well.