I use slackpkg+ which is an addon to the default package manager that allows you to install packages from community and third-party repositories.
And sbopkg which gives you a TUI frontend to install Slackbuilds (Slackware-specific build scripts for building from source).
Neither offer dependency resolution, which I don't really need anyway.

Now that I know how Slackware works and what its quirks are, I don't really have any issues with it. But it's pretty hard to figure that out when you're coming from more modern distros. It throws curveballs at you, like not booting after a kernel upgrade if you forget to copy the new kernel to your EFI partition and recreate the initramfs.
Most online documentation is wildly out of date and googling is no help due to how few users there are.
It took a while till I figured out the README files that come preinstalled with the distro are actually the official, up-to-date documentation and very helpful, and also that the place where most users (including the maintainers and author of the distro) gather and answer questions is the linuxquestions.org forum.