Here's the code: https://github.com/mattermost/platform From the look of the screenshots ( http://www.mattermost.org/70-2/ ), I'd say there are some copyright concerns with the styles. This isn't a Slack alternative, it's a Slack clone. That's very problematic from a copyright stance. Why not create your own design style? Gogs had (has?) this same issue: https://github.com/gogits/gogs/issues/1069
> That's very problematic from a copyright stance why? they didn't copy slack (i assume) - it just looks similar. Slack doesn't (and shouldn't be allowed) own a look and feel, as long as the implementation of it is cleanroom.
I have no idea if Slack could actually win a case, but in the US (where both companies appear to be headquartered) they do have some rights to look and feel as part of trademark law.