When comparing Cairo-Dock vs Krunner, the Slant community recommends Krunner for most people. In the question“What are the best app launchers for UNIX-like systems?” Krunner is ranked 8th while Cairo-Dock is ranked 14th. The most important reason people chose Krunner is:
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Specs
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Pros
Pro Easy to tweak and make your own themes
Drag and drop, change icons, use effects, etc. It's fun to play with. It's not a basic dock program and the GUI is good.
Pro Cairo-Dock session
Users can choose to launch a stand alone Cairo-Dock session where the dock also serves as a taskbar where all apps are launchable such as in any other DE session. There is a composited version and one without.
Pro Popular and usually found and installed from a distros repo
Due to the popularity and how long Cairo-Dock has been around it is more often than not found in a distros repos, which is very convenient to get the app installed.
Pro Easily themed
Cairo-Dock has built in settings to install and use themes for the dock and icons. Definitely more robust in this are than most other docks available for Linux.
Pro Opens folders/files also
Just by typing name of file or folder, it will give recommendations
Pro Extensible with plugins
Krunner can be extended with the use of "runners" which are essentially plugins for the app launcher to allow for extra functions.
Pro Fast
As it is written in Qt QtQuick using QML.
Pro Lots of handy features
Such as a fully featured calculator, file opening, browser functions, currency conversion, date/time functions, etc.
Pro Great integration with Plasma, developed by KDE
Pro Can be used to open websites
By just typing an URL into the text box users can have the site open in their default launcher.
Pro I'm able to find open tabs from browsers with KRunner which is very nice
Even supports edge browser.
Cons
Con No updates since 2016
Certainly no PPAs for modern releases of Ubuntu.
Con Poor/No system theme or icon integration
Docks use their own theme, own theme colors, icons, layout's and theme engines.
Con Hard/Underwhelming to configure
Cairo dock proposes a feature rich tool, tweakable to any degree. The configuration menus are at times inappropriate, shallow and uninteresting, complex to navigate, and prefab-centric. Rarely offering a satisfying preset, and always unsatisfying to tweak.
Con Can be heavy on resources for weaker systems
Cairo-Dock is more on the heavy side when compared to other docks, which is something to keep in mind for those that are on low resource systems.