As a remote-only team, we've now been using Tandem for more than 2 years. Besides Tandem we're using Slack for chat-based, async communication and Notion for documentation and collaboration (i.e. anything that is not ok to be gone within a day, like stuff written in Slack).
Especially for a remote team Tandem really bridges the gap. You have the presence of your team in the same way as ICQ and MSN, and everyone is easily accessible. Prior to Tandem people tended to schedule an event in the calendar resulting in 30-45 min blocks and a big mental hurdle that in an office environment would've just been solved by seeking eye contact with someone. This is what Tandem does fix! Would not run a remote team again without it.