Multiple cursors for Emacs. This is some pretty crazy functionality, so yes, there are kinks. Don't be afraid though, I've been using it since 2011 with great success and much merriment.
I use this package every day, and have been doing so for years. It just works. At least, it works for all my use cases. And if it breaks somehow, I fix it.
However, it has become painfully clear to me that I don't have time to fix problems I don't have. It's been years since I could keep pace with the issues and pull requests. Whenever I try, I keep getting feedback that my fix isn't good enough by some standard I don't particularly care about.
So, I have closed the issue tracker and the pull requests. I hope you can happily use this package, just like I do. If it doesn't work for you, then I'm sorry. Thankfully Emacs is infinitely malleable, you can probably fix it yourself.
The package depends on the cl-lib package, so if you do not use package.el or have a recent Emacs, you would need to install that too: see GNU ELPA.