A better calculator than more than half of other applications. Mainly, because it works great in a **multi-lingual** context. You may need to deal with copying numbers that may contain either "dots" or "commas" as decimal seperators. Qalculate provides configuration to deal with it. See the required settings here: https://forums.linuxmint.com/viewtopic.php?p=2508130#p2508130
Doesn't use commas and periods correctly. There is an option to use only periods for decimals, but then it doesn't display correctly.
Has RPN mode! But the HP-15C simulator is MUCH better: https://hp-15c.homepage.t-online.de/content_web.htm