Gentoo is a 'roll-your-own' Linux distribution. The typical flow is to load a barebone system (basically a compiler and supporting tools), and build every package you want from source.
On the upside, you can control everything you want—in particular, you can compile whichever program you want with any available set of options. For instance, if you despise JPEG for whatever reason, you can build GIMP without jpeg support. Therefore, you can have a lean system with only what you'll need.
On the downside, deploying Gentoo is hard and time-consuming. Installing packages builds everything from source, so it takes a lot more time.
I like it because it has a lot of things I like (for instance, I can swap between any GCC version from 4.1 to 4.9 and any Python from 1.5 to 3.5).
Because Gentoo requires a decent level of savvy and experience to install (and you'll probably become comfortable with the compilation process), this page is more to say that compared to installing Gentoo itself, getting Amber built on it is cake.
Just make sure that you have the following packages installed:
flex, tcsh, python2, bison, mpich2, and probably others I can't think of right now. I didn't have to install any other packages after I had my machine set up the way I wanted.
When building software, you should have the following USE flags set:
- tk — At least for Python2, this provides Tkinter so xparmed.py will work
- fortran — You need a Fortran compiler, and Fortran bindings for any package Amber needs.
- xinerama — This is not really related to Amber, but if you want to use multiple monitors it is a must-have.