I don't know if Stride was losing out to Slack, or if it was losing out to the FOSS competitors like Rocket, Mattermost, and Zulip. I've found Rocket and Matter

I don't know if Stride was losing out to Slack, or if it was losing out to the FOSS competitors like Rocket, Mattermost, and Zulip. I've found Rocket and Mattermost to work well for small teams (no experience with medium or big deployments). With the FOSS alternatives plus the more fringe competitors like Ryver, Glip, and Twist, plus related tools from Dropbox, Basecamp, etc., it's hard to see there being a market for Stride.