Android RPN app?

[Nigel (UK)]

Two main ones:

• Free42 (of course!). I first used this on a Palm Zire Z22 about a thousand years ago and I've not been without it since. Available on a huge number of platforms (including the DM42 SwissMicros calculator if you want a version with a real keyboard). Good things: high precision (more than 30 significant figures); constant bug fixes and new features from Thomas Okken; an extremely reliable simulation of the HP42S. Bad things - nothing, really. It is basically an HP42S and if this isn't what you want then it might not suit you, but otherwise it's great.
• Acron RPN Calculator FREE (there's a paid version as well, but try this first). I love this because as well as showing the stack it shows how each stack level has been reached in the form of an algebraic expression. It isn't programmable, however. If you display the complete keyboard on the screen at once it can be a little overwhelming.
  

(Both used on Android.)

Nigel (UK)