Linux

Artix Linux. Basically Arch without systemd. It has four options for alternative init systems, so you get to see how it compared to systemd (ultimately it shows how a more minimal init approach is all you need in place of systemd, and where systemd has stepped outside of init into what should be part of the OS space, like elogind, etc.)

The Artix team have done an amazing job of writing various init scripts to keep the distro comparable with Arch, have written alternatives to systemd modules, like replacing elogind with their own implementation, seatd, and IMHO is the defacto standard for how you implement a non systemd distro.

Working without systemd, even if you like it from a sys admin standpoint, teaches you what you lose without systemd, which for the average user isn't much. I game, code, administer web servers, etc., all without missing a beat on Artix Linux, and it honestly has taught me so much about Linux after I switched from Arch.

I would consider jumping to Gentoo or Void out of curiosity, but Artix is where I'll be staying for the foreseeable future.

Void Linux! It's a very simple, completely independently distro without a dependence on a corporate funded project. It uses runit in place of systemd (I don't mind systemd but it seems a lot of people just like runit better for being smaller, neater, and very reliable, which is cool)

It has a "stable rolling release" update model and provides vanilla packages. And the package manager xbps can install pre-compiled binaries or function more like portage or BSDs ports system for building from source (full disclosure, I've never used any of those nor the functionality in xbps so I don't understand it super well). Oh and the community is helpful, and the documentation is pretty strong and doesn't always just give you commands to run blindly (as someone who is trying to get more confident in the terminal I find that helpful)

The project has a very "less is more" philosophy which I really appreciate.

My one disappointment is that there isn't a package kit implementation for xbps so I can't use the graphical software store provided by my desktop environment :(

SnowflakeOS.

Based on NixOS, its goal is to be more user-accessible than NixOS, shrinking that learning curve, and still being just as declarative and stable.

It's still in Alpha, though, so not yet ready for the aforementioned users.

Fedora Kinoite: the most stable update and package mechanism there is.

Even though the packages are really new, it is still stable and you always have a rollback.

Even more, you can reset the system, and we are experimenting with factory resetting too. Resetting means as long as your system has some bootable backup, you can get back to 100% vanilla but current version, without reinstalling.

Slackware!

"But it has no dependency resolution."

It does, but it's optional. And it really isn't an issue like you'd think coming from other distros. It uses a completely different paradigm: You don't have to care about dependencies at all, cause you already have all of them taken care of after a default install.

It comes with batteries, meaning the default install includes everything you need for general computing. It's the Anti-Arch. You don't have to install a DE, your editor of choice, an office suite, TeX environment, image editing software, or configure a LAMP stack. You already have it. Granted, it works best if the default software selection suites you, and it's a bit unconventional.
But in case you do need more, Slackbuilds are there for you, which work very similar to Arch's AUR.

Also, it follows the KISS philosophy to the letter. It's basically just a distribution of software in the classical sense, plus some bash scripts written by the benevolent dictator Patrick Volkerding himself.

Newcomers will often be put off cause the online documentation is very lacking and outdated. But again, Slackware is different. Documentation is included in the form of easy-to-understand and descriptive text files, which are also written by Pat himself, and are found right where you'd be in the filesystem when you need them. For more specific stuff, ask on linuxquestions.org, where, again, Pat is actively posting.

It's not for everyone, or even for many people, but IMO still fills a niche for people who want a system that is as simple as Arch, as stable as Debian, and a blast from the past of Linux (without the hardware issues).
There's a "Slack" way to do things, and once you get it, the distro becomes the easiest to maintain of them all. Cause almost literally nothing ever changes.

Void Linux. It's simple, lightweight (the base system doesn't come with much, only an installer you run from a TTY interface), and I like its package tree/templates system. Contributing to packages is pretty straightforward, however you need to be patient, as maintainers aren't as available as the ones from other (more popular) communities. Their IRC channel on Libera is also pretty helpful, when you run into problems.

NixOS:

• Largest and most up to date package repository (no need for flatpack/appimage/snap ect)
• Reproducible
• Declarative
• Rollbacks you can select at boot time
• No dependency conflicts

I think it will easily be the number 1 distro if/when they can :

• the steep learning curve (e.g. have a gui installer EDIT: As in a GUI software centre)
• documentation
• have more tools use nixos and have nixos in mind (e.g. there are a couple of tools that didn't work for me because of specific C libraries not beeing present/configured on nixos that are present on other distros. some libraries implicitly expect these to be present).

https://garudalinux.org/ , based on archlinux with calamares installer and optimized binary packages, plus zstd-compressed btrfs and snapper (easy rollbacks for updates from grub items). And many other thingys. Oh, and as default kde theme a fork of my favorite, Sweet.

Not exactly Linux, but Haiku. Been rooting for them for years. Because I used BeOS and I must admit, it was light years ahead of the rest. Haiku though does not seem to be doing too well.

May as well contribute my own 😜.

I'm an absolute sucker for exquisitely hardened distros. Hence, distros like Qubes OS and Kicksecure have rightfully caught my interest. However, the former's hardware requirements are too harsh on the devices I currently own. While the latter relies on backports for security updates; which I'm not a fan of. Thankfully, there is also secureblue.

Contrary to the others, secureblue is built on top of an 'immutable' and/or atomic base distro; namely Fedora Atomic. By which:

• It's protected against certain attacks.
• Enables it to benefit from more recent advancements and developments that benefit security without foregoing robustness.

If security is your top priority, Qubes OS is the gold standard. However, secureblue is a decent (albeit inferior) alternative if you prefer current and/or 'immutable'/atomic distros.

Chimera Linux (not to be confused with ChimeraOS, a variant of SteamOS). It introduces itself like this:

Chimera is an independent, general-purpose, rolling-release Linux distribution developed from scratch. It utilizes a FreeBSD-based userland, musl C library and the LLVM toolchain, along with the dinit service manager. Its primary focus is correctness, consistency and simplicity, but not at the expense of feature set; its primary desktop environment is GNOME

It’s worth mentioning that it’s a Linux without GNU (though not for the sake of being that). In general I think projects like this one has a value from a ecosystem diversity perspective too, which also has become immediately apparent when Chimera Linux wasn’t hit by the two last security issues I learned about (the recent SSH regression and the xz debacle).

I’m particularly impressed with their relatively lean setup, but I haven’t had opportunity to use it yet. It’s a bit too immature for my desktop use and I’m already happy with the server I have so it makes no sense to switch.

Funtoo sounds interesting but I haven't tried it.

Fedora and Debian