Tchap is just Element/Matrix with some gov specific features.

We use Mattermost at work, and apart from the mobile app being a bit shit, and search being kind of useless, it's easily as good as Slack. In some ways it's better, e.g. you can use proper Markdown in messages instead of Slack's Mrkdwn abomination that doesn't even allow links.

I wish they would improve search though; it's kind of a critical feature in a company.

? I put Slack into non-rich-text-editor mode and use standard markdown link syntax dozens of times a day

Well maybe they've added that in the past 2 years but certainly 2 years ago you could only add links using rich text mode.

search is the #1 feature I use in our corporate slack (huge, huge instance).

without search it's useless.

It has search, it's just very basic. Only searches for exactly what you put etc.

I remember Slack's search being equally crap when I last used it a couple of years ago.

sounds exactly like slacks search, except slack also doesn't find exactly what you put in sometimes... (think the indexing isn't very fast because sometime a day old message is impossible to search for)

slack search has been awesome for me. if you want exact search, put it into quotation marks.