As said, this is a world not travelled for me, so please bear with me, and feel free to give me a proper beating if I get anything wrong. HP has made available a few of its Reverse Polish Notation calculators for the iPhone and Windows. The iPhone gets the 12c financial calculator and the 15c scientific calculator, while Windows gets the HP 35s scientific calculator, the 12c Platinum financial calculator, and the 20b business-consultant calculator.
Image credit: CNet/ Stephen Shankland
They're not exactly what you'd call cheap; the 12c comes in at USD 14.99, while the 15c goes for USD 29.99. It is important to note, though, that "real" versions of these calculators are a lot more expensive (some still get made). Since these software variants are a lot cheaper to make, this is a clever move by HP. The Windows versions work with the touchscreen PCs HP puts out, making it all a little bit more realistic.
I love the attention to detail HP has put into these applications, and I'm sure many geeks with fond memories of these calculators will appreciate that HP is making them available software-wise.