Synaptic is a graphical package management program for apt. It provides the same features as the apt-get command line utility with a GUI front-end based on Gtk+.
The pacman package manager is one of the major distinguishing features of Arch Linux . It combines a simple binary package format with an easy-to-use build system. The goal of pacman is to make it possible to easily manage packages, whether...
pacman (package manager) vs Octopi opinions
While pacman is the package manager, Octopi is a GUI using pacman. Not really the same thing.
Graphical Package Manager for Manjaro Linux (based on libalpm).
Pamac vs Octopi opinions
Pamac and Octopi are both GUI ways of interacting with pacman, the package manager in Arch and Manjaro Linux distros. Both are excellent, but Pamac is probably the more user-friendly by a small margin. Octopi comes with Manjaro's KDE Plasma version; Pamac with the XFCE, Mate and other GTK-derived desktop environments.
PAMAC is better laid out and has some very practical features missing from Octopi, such as showing history of installed/removed packages and the ability to tell it to ignore updates for some packages. I suggest viewing some YouTube clips to get an idea of which interface is more user-friendly also, i prefer PAMACs.