Are there any "groups" in Stack Exchange just like we see in Reddit?

Surprisingly I couldn't find anything in the faq about this.

Stack Exchange is divided into (currently) 182 Q&A communities (the number on that page should be updated), commonly referred to as "sites". Here is a list of them. I guess they are similar to subreddits, but obviously we have a lot fewer of them. There may be some overlap between sites but unlike subreddits, it's usually minimal.

Each site has a corresponding meta site for discussion about/support for/etc. the site; the one you're on now is about the entire network, so you've come to the right place with your question.

Questions on a site are further organized by tags, and especially on larger sites like Stack Overflow, subcommunities may form around the largest of those tags (usually programming languages).

Rather than having discussions across different subreddits, practically we run as separate, pseudo-independent sites. Sometimes we have overlaps in topicality - consider our general computing site Super User where I'm a moderator, Unix and Linux and Ask Ubuntu have topics that nest, and sometimes we overlap with Server Fault. A good way to get an idea of what sites we offer is to take a look at our site list, and if you find a topic that catches your attention that a site covers, go take a look at existing posts there, and the help to see if it's a good fit. We have a broad array of sites that cover both technical and non-technical topics.

I'd note that there's a common culture - for example, we're not a discussion board (mostly - there's an experiment with one at stack overflow), we're mostly about focused, practical questions and clear, self-contained answers, but also occasional quirks with specific sites according to their needs. It's worth spending a little while looking around to understand how things work for best results.