Arch Wiki: https://wiki.archlinux.org/index.php/clipboard

Anamnesis — Clipboard manager that stores all the clipboard history and offers an interface to do a full-text search. It has both a command line and GUI mode available.
http://anamnesis.sourceforge.net/ || anamnesis

Autocutsel — Command line and daemon interfaces to synchronize PRIMARY, CLIPBOARD and cut buffer selections.
http://www.nongnu.org/autocutsel/ || autocutsel

Clipboard Indicator — Clipboard manager extension for GNOME Shell. Adds a clipboard indicator to the top panel, and caches clipboard history.

ClipIt — Fork of Parcellite.It has both a command line and GUI mode available.
https://sourceforge.net/projects/gtkclipit/ || clipit
Cliplt Homepage: http://clipit.rspwn.com/

Clipman — A clipboard manager for Xfce. It keeps the clipboard contents around while it is usually lost when you close an application. It is able to handle text and images, and has a feature to execute actions on specific text selections by matching them against regular expressions.
https://goodies.xfce.org/projects/panel-plugins/xfce4-clipman-plugin || xfce4-clipman-plugin

Clipmenu — Dmenu based clipboard manager
https://github.com/cdown/clipmenu/ || clipmenu

Clipster — A lightweight, command-line-driven clipboard manager, written in Python.
https://github.com/mrichar1/clipster || clipster-git

CopyQ — Clever clipboard manager with searchable and editable history, custom actions on items and command line support.
https://github.com/hluk/CopyQ || copyq

Glipper — Clipboard manager for the GNOME desktop with many features and plugin support.
https://launchpad.net/glipper || glipper

GPaste — Clipboard management system that aims at being a new generation Parcellite, with a modular structure split in a couple of libraries and a daemon for adaptability. Offers a GNOME Shell extension and a CLI interface.
https://github.com/Keruspe/GPaste || gpaste

Keepboard — Cross-platform clipboard manager. Saves text, image and file clipboard items.
https://sourceforge.net/projects/keepboard/ ||

Klipper — Full featured clipboard manager for the KDE desktop.
https://userbase.kde.org/Klipper || plasma-workspace

Parcellite — Lightweight yet feature-rich clipboard manager. It has both a command line and GUI mode available.
http://parcellite.sourceforge.net/ || parcellite

Pasteall — Clipboard monitor simple and functional (with notifications in Portuguese).
https://github.com/ShyPixie/Pasteall || pasteall

Qlipper — Lightweight and cross-platform clipboard history applet based on Qt.
https://github.com/pvanek/qlipper/ || qlipper

Xclip — A lightweight, command-line based interface to the clipboard.
https://github.com/astrand/xclip || xclip

xcmenu — Clipboard synchronizer developed for window manager users.
https://github.com/dindon-sournois/xcmenu || xcmenu-git

xsel — Command-line program for getting and setting the contents of the X selection.
http://www.vergenet.net/~conrad/software/xsel/ || xsel


What’s the difference between Primary Selection and Clipboard Buffer?
Wikipedia / X Window selection
How to toggle or turn off text selection being sent to the clipboard
Arch Wiki / Clipboard