Free42 by Thomas Okken
Ranked 5 of 7 calculator apps by recommenders
A free emulator of the HP-42S RPN scientific calculator that runs on phones, favored by people who like RPN calculators.
A free emulator of the HP-42S RPN scientific calculator that runs on phones, favored by people who like RPN calculators.
7 people gave an opinion
- recommend it
- 7
- criticize it
- 0
- approval share
- 100%
Recommended in 5 of 13 months
- November 2025: recommended
- December 2025: not recommended
- January 2026: not recommended
- February 2026: recommended
- March 2026: not recommended
- April 2026: not recommended
- May 2026: recommended
- June 2026: recommended
- July 2026: not recommended
- August 2026: not recommended
- September 2026: not recommended
- October 2026: recommended
- November 2026: not recommended (month in progress)
Why it doesn’t carry the badge
- 7 people recommend itNeeds 10 or more, not met.
- Nobody criticizes itNeeds 2 to 1 or better, met.
- Recommended in 5 of 13 monthsNeeds 4 or more, met.
The same three rules apply to every product, and the badge can’t be bought. How the badge works
What people say about it
The reasons people give, with the number of comments that give each one. Open a reason to read what they said.
Why people recommend it
Each mark is one comment
Free and GPL licensed
“a great choice is the Free42 project by Thomas Okken, which is a GPL-licensed project that is entirely compatible with the HP-42”
Comment from 18 May 2026 in “Graphing Scientific Calculator Based on the ESP32” “Thomas Okken's free42 is a great, free HP42S emulator which runs on iOS.”
Comment from 3 Feb 2026 in “Ask HN: Do you still physical calculators?” Faithful HP-42S emulation
“a great choice is the Free42 project by Thomas Okken, which is a GPL-licensed project that is entirely compatible with the HP-42”
Comment from 18 May 2026 in “Graphing Scientific Calculator Based on the ESP32” “Thomas Okken's free42 is a great, free HP42S emulator which runs on iOS.”
Comment from 3 Feb 2026 in “Ask HN: Do you still physical calculators?” Used on phone daily
“up to and including the Free42 on my phone today”
Comment from 3 Jun 2026 in “HP re-releases classic computer science calculator: The HP-16C” “If I don't have it in hand I use Free42”
Comment from 3 Jun 2026 in “HP re-releases classic computer science calculator: The HP-16C”
Other calculator apps people recommend
The four most recommended other calculator apps, with the same counts for each, so you can compare like for like. The tick on each bar marks the 2 to 1 line the badge needs.
| Product | Recommend | Criticize | Approval | Months | Owned | Badge |
|---|---|---|---|---|---|---|
| SpeedCrunch | 13 | 7 | 65% | 4 | — | — |
| Windows Calculator | 9 | 34 | 21% | 5 | — | — |
| Qalculate | 9 | 0 | 100% | 5 | — | — |
| Can I Run AI locally? | 9 | 14 | 39% | 1 | — | — |
| Free42 by Thomas OkkenThis page | 7 | 0 | 100% | 5 | — | — |
What people said
7 of the 8 comments that mention it, newest first. Each links to the original comment.
“up to and including the Free42 on my phone today”
“If I don't have it in hand I use Free42”
“a great choice is the Free42 project by Thomas Okken, which is a GPL-licensed project that is entirely compatible with the HP-42”
“It's great if you like RPN calculators.”
“Thomas Okken's free42 is a great, free HP42S emulator which runs on iOS.”
“My other favorite calculator is free42”
“I really like the unlimited stack option that can be enabled in Free42”
Counts come from 1,795,640 Hacker News comments, November 2025 to November 2026. How we count. Report a mistake.