When I display, pacman -Sii galculator, the URL is http://galculator.sourceforge.net/, the Packager has an archlinux address, and it Depends on gtk3. When I go to the URL, it says:
Please note - galculator moved away from sourceforge. From now on, github is our main choice for collaboration and communication!
I looked at the PKGBUILD and it is referencing the sourceforge link.
I selected this calculator as a replacement for kcalc when I switched to XFCE. I will get an error message at the console or ~/.xsession-errors saying:
Unable to locate theme engine in module_path: “murrine”.
pacman -Ss murrine says the above is a gtk2 engine.
What is the appropriate reporting action regarding the url update and the error message, if any?
I do realize the source hasn’t been touched in ages. Yikes! 
Your best option is to contact the maintainer at their GitHub page and file a bug report. 
@Aragorn Thanks.
@jrichard326 Thanks. I totally missed that. Even my favorite site to find alternatives said it’s currently dead.
@Locutus Thanks. It is funny you mentioned that. I’ve been leery of installing Qt apps (short story, trying to reduce telemetry, commit to gtk, etc, etc), but I looked over qalculate/qalculate-gtk. One thing I look for in a caculator is easy conversion between number bases, binary to hex, hex to octal, etc. I was going to give up on qalculate-gtk, but figured out I needed to use the functions bin(), hex()…, and that the dropdown represented the output.
I found all the above helpful for different reasons. Can I mark a topic as solved, without picking one? 
Indeed. I was bored so I did.
FS#72719 - [galculator] is dead
EDIT: …and so is @philm apparently, he already commented. 
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gnome-calculator might be an option.
FYI, gtk2 is now dropped with galculator 2.1.4-6.