This short post is a response to a question from @davidmuseums, regarding Trello and Slack; a pair of applications that are very useful when working on Agile projects (or just working in digital in general). As I'm not keen on epic Twitter threads, I thought it would be easier to just answer it here.
This post is not intended as a 'What is Trello/Slack and how can it make my life better blog'. To learn more about that, I'd recommend Adam Koszary's Medium piece on his experience using these tools at the MERL . David's question however, pits the tools against each other:
The answer in my opinion is that neither is better than the other. Each tool has a different purpose and in fact, can be easily integrated together to harmonise a planning and communication workflow for the a team, by considering them as tools for the following purposes.
- Trello is where tasks are organised and scheduled.
- Slack is where we discuss, debate and throw ideas about for how to do/solve these tasks and co-ordinate them.
- Integrating the apps means we are able to link our tasks to our discussions and in turn ensure our schedule and priorites remain at the front of our communication.
From a technical perspective, this integration is fairly easy to manage, as the apps support each other through the use of Trello Power-Ups and Slack Integrations. For example, lets say we're having a conversation about upcoming blog posts in our Slack blog channel, and a discussion thread has settled on a topic and what should be covered in it. From the blog channel in Slack, I'm able to issue a command to Trello to create a card for the blog board (which is linked to that channel)
/trello set-list October
/trello add @Terry Pastels Blog Post
/trello set-due next Wednesday at 2PM
This creates a card, assigns it to me and sets it to be due for next Wednesday, all from the Slack interface. Once its been created I can then inspect the card from Slack, add comments and even link the conversation we've just had about it to the card. 
In the reverse direction, Trello can also be configured to send information back to Slack as changes arise. Lets say for instance, that blog was moved to the back-burner becuase more pressing content was scheduled. When the due date is removed and the card is moved into the Someday pile, a notification will come up in the Blog channel on Slack. That way, all team members can see how the plan is changing and when changes have been made.
Users can also send card links to channels to solicit comments - so if I had an idea sketched out on a Trello card and wanted a few comments, I could just post the card link to the channel and all the information will be made available. Colleagues can then go to the card in Trello to comment, or attach their comments using the Slack commands.
These are the main ways that Trello and Slack can work together and the two tools together can produce a pretty smooth workflow, especially as we can capture the conversations and discussions onto the cards. I'm yet to see how it will work on other boards and across teams (especially getting people used to the command ideas). If you are following Agile methedology as part of a team, its well worth trying out Slack and Trello as a pair, rather than seeing them as rivals.