The story is a bit complicated. There was conda by the anaconda company written in Python. Then the open source ecosystem conda-forge is a conda channel with CI build bots. Then mamba being in the same umbrella under conda-forge is a drop-in replacement of conda written in C++ (this is actual drop-in that `alias conda=mamba` should work.) Then now conda uses libmamba as the solver to speed it up.

Then the author of mamba spin it off to pixi, a rewrite in rust with different philosophy on how environments should be located and activated, with full compatibility with conda environments.

Conda always supports installing packages from PyPI via pip (when it isn’t available from conda channels for example.) and pixi support PyPI packages via uv. That makes pixi fast. (There are other optimizations done outlined in their blog post making it much faster than even mamba.)

If anyone uses any non-pure python packages, then conda is the way to go. Package manager choice (conda/mamba/pixi) is secondary.

The problem with PyPI is the lack of gate keeping. That coupled with lack of standard way to package non pure python packages makes environments leaking (see comments on errors encountered in exotic or old environments), and/or non-reproducible (especially when people is distributing source only and doing crazy things in setup.py to bootstrap their environments including compilers.)

In conda land, the conda-forge channel has pretty good gate keeping to ensure quality, such as being constrained properly, licensed properly (PyPI maintainers sometimes didn’t include the necessary license file in the distribution), environment isolated properly, etc. it’s not bullet proof as there is official bot that maintainers can use to auto-merge changes from PyPI that has wrong version constraints for example.

The problems that no tools can solves right now are centered around PyPI: deal with packages not available in conda, and releasing packages virtually mandates releasing on PyPI first.

When installing packages available on PyPI only through conda, there are some of its dependencies still available through conda. AFAIK, no package manager will use conda packages to fulfill the PyPI package dependencies. You can manually add the conda packages to resolve dependencies, risking not subjecting it to the right version constraints.

And when you author an open source python package, even if your setup relies on conda channels only, you most probably would/need to release it on PyPI first (releasing on conda-forge channel virtually mandates a presence at PyPI first). Then you need non-conda tools to help you. This is why Rye would still be useful to people like me, and worth checking out.