Can you step back further and explain what Renovate and its competitors like Mend actually do, and what kind of tasks people use them for?

To help you automate dependency updates, similar to dependabot.

https://www.mend.io/renovate/

https://github.blog/news-insights/product-news/keep-all-your...

Mend is not a competitor, renovate is the software, mend is the company.

They are tools that automatically check your repo for dependencies and create PRs when there are updates. It supports a wide range of package managers and other places dependencies may be specified.

Dependabot is another solution which is more „GitHub-native“ maybe.

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In short, Renovate (by Mend) is a dependency manager for software projects. It watches your repository for outdated libraries, packages, and frameworks and opens Pull Requests to update them.

See also: https://news.ycombinator.com/item?id=40011111

(a blog post I wrote, prior to joining Mend and working as a Renovate maintainer)