So, I've seen a lot of people struggle with getting modpack servers working, even if the instructions are very clear from the modpack makers, no matter how much help they get from the CurseForge Discord..
And with that, I started a (yet another) little project of mine, first of all, because I wanted one myself, to see if I could pull it off, using nothing but the available APIs, and some code of mine.. spoiler, I made it work.
First off, I'm gonna say it, it's not perfect, there will be modpacks that it will fail to at least start, because of the nature of Minecraft modding, where the devs doesn't add code to bail out if they are intended as client-side mods only. And the reason this software will fail because of that, is because they are not tagged as client-only mods (you can't mark them as such).
And, no it's not a GUI based application, it's a CLI (Command Line Interface), to make it usable on most platforms.
Edit: Previously, we didn't have a macOS version, but with 1.0.1, we have support for macOS as well!
But, if an image speaks more than thousand words, what would a video do then?
The project is of course open source, and can be found in the CurseForgeCommunity GitHub organization. So, if you have any questions, feature requests or bug reports, be sure to get them in there!
We also have a documentation site available for this project, which will tell you the absolute basics on how to use it. And it's available here.
Now, get out there, create your own server, and good luck with the mining! <3