Casrion, on Windows.

For Windows 10 and 11, 64-bit.

Download, run, click past one blue box. Then it sits in your tray and every key below works in every app you have open.

Download for Windows Free, no email, no account.
Runs the installer you already trust.

The blue box

Windows will say it protected your PC. That is SmartScreen, and it says it about any installer whose author has not bought a code signing certificate. That certificate costs more per year than this app makes, which is nothing, so I have not bought one.

Click More info, then Run anyway. It happens once and never again. Nothing was found, nothing was scanned and flagged. It is a name Windows does not recognise yet.

Every key

All of these work everywhere: your browser, a PDF, Word, a terminal. Inside the app, CtrlShiftH puts this same list on screen whenever you want it.

Copy something first, then press

Anything you can select and copy, in any app you have open.

Keep it as it is	Ctrl+Shift+C
Keep it as a big heading	Ctrl+Shift+1
Medium heading	Ctrl+Shift+2
Small heading	Ctrl+Shift+3
Keep it as code	Ctrl+Shift+K
Keep it bold	Ctrl+Shift+B
Keep it italic	Ctrl+Shift+I
Keep it red, green or blue	Alt+R/G/B

Nothing to copy

These make something new rather than keeping something you found.

Drop in a screenshot Snip it with Win+Shift+S first, then this.	Ctrl+Shift+V
Start or stop a voice memo	Ctrl+Shift+M
Open a whiteboard and draw	Ctrl+Shift+D
Type a quick note from anywhere	Ctrl+Shift+Q
Start a new paragraph	Ctrl+Shift+N
Undo the last capture	Ctrl+Shift+Z
Redo it	Ctrl+Shift+Y

Explain a selection

Highlight first. No need to copy anything for this one.

Explain what I highlighted Two taps, quickly, without holding it down.	Ctrl,Ctrl
The same thing, if you prefer a chord	Ctrl+Shift+E

Inside the whiteboard

Only while the board is open and in front of you.

Undo a stroke	Ctrl+Z
Put it back	Ctrl+Y
Close without saving	Esc

The explain thing

Highlight anything, anywhere, press CtrlShiftE, and a small window tells you what it says. It reads the screen around your selection first, so it knows a loose symbol belongs to the formula three lines up.

Tapping Ctrl twice, quickly, does the same thing. It only counts when Ctrl goes down and back up with nothing pressed in between, so copying and pasting never sets it off by accident.

The first time you use it, it downloads a small model, once. After that it works on a plane. Nothing you highlight is ever sent anywhere, because there is nowhere for it to be sent to.

When something acts up

Windows says it protected my PC.: SmartScreen. More info, then Run anyway. Once.
A shortcut does nothing.: Something else on your machine grabbed that combination first, and whoever registers it first wins. Games, capture tools and clipboard managers are the usual suspects. Close the suspect and try again.
I closed the window and it vanished.: It did not. Closing the window is how you get it out of the way while it keeps capturing. It is in the tray, next to the clock, possibly under the little arrow. Right click there to actually quit.
Where do my notes live?: Markdown files in folders you picked, with screenshots, voice memos and whiteboards in an assets folder beside them. Nothing is in a database. They are just files.
How do I update it?: Run the new installer over the old one. Your notes and settings are untouched.
Does it phone home?: No. There is no account, no telemetry, no update check. The one and only download it ever makes is the explain model, and only if you ask for it.