The RPN Calculator browser extension, developed by Mike Conca, adds a convenient reverse Polish notation (RPN) calculator as a browser action button. This free extension is available on the Chrome platform and falls under the category of Browsers with the subcategory of Add-ons & Tools.

RPN calculators, also known as postfix calculators, have a unique way of taking operators after the operands. Unlike traditional calculators, where you would enter "2 + 3 =", on an RPN calculator, you would enter "2 Enter 3 +". This notation can result in fewer keystrokes in a series of extended operations.

While it may seem unfamiliar at first, once you get used to it, you'll find it to be a more efficient way of performing calculations. In fact, HP had a series of highly popular RPN calculators in the 1970s and 1980s.

However, there are a couple of known issues with this extension. Firstly, the calculator doesn't automatically get focus when displayed. Secondly, it only supports keyboard input, so clicking on keys and commands doesn't work.

Overall, the RPN Calculator browser extension offers a convenient way to perform calculations using reverse Polish notation, but it could benefit from addressing the known issues to enhance the user experience.