https://heldercorreia.bitbucket.io/speedcrunch/
The only calculator you need! It has custom units, functions, it's quick, light, stays on top.
I used speedcrunch for a long time but ended up switching to Qalc and haven't turned back.
Yes both!
I use Qalc for unit conversions (I often need to convert measuring units without acces to internet) and SpeedCrunch for everything else