Ytdyklly

There are a couple of utilities to emulate the Unix-a-like key composition chords under windows. Allchars is one, which is also F+OSS, though I've not actually tried it myself yet (it is one of the many utilities in my "to try later" bookmark folder).

On Windows, AllChars should do what you want. I have been using it for the exact purpose you describe for almost a year now.

Caveat: If you install AllChars and your keyboard starts to behave weirdly, try one of the other versions they offer, possibly the alpha/beta. They all seem to have different issues with the different versions of Windows out there. But one of them should work with whatever you use.

There's also Freecompose, found on code.google.com, but it has that annoying beep everytime you start compose mode.

Accent Composer looks promising, and I hope to try it some time.

Update:

Actually AllChars seems to do what I need (despite the web site saying it doesn't; I guess the web site's info is out-of-date compared to the latest version), and it's free. So I won't bother with Accent Composer.

You can use United states-International keyboard layout, You can type accented characters easily without any special software.

` + a = à

' + c = ç

" + o = ö

I don't think you can use it for € and m-dash though

Within MS programs (word, outlook, etc.) you can type ctrl + : o to get ö and ctrl + ` e to get è

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If I understand what the Compose key does in Linux, the Windows equivilant is to press Alt Gr along with a key such as A to produce á or Á, E to produce é or É etc.

You can also hold down the left Alt key along with a number code on the numerical keyboard which will produce many symbols such as

Alt+1 = ☺

Alt+2 = ☻

Alt+3 = ♥

Alt+4 = ♦

Alt+5 = ♣

Alt+6 = ♠

Alt+7 = •

Alt+8 = ◘

Alt+9 = ○

Alt+1,0 = ◙

There are thousands and after a quick look, I cannot find a complete list - I have found this guide that looks good - (and found it from this link) however there are many and you may find better.

Also, You can go in to Character map (either through Accessories or Run > "Charmap"), and click on a symbol and see what it's shortcut keystroke is - (it is not available for everything).

The compose function is not exactly the same as a dead key.
Strictly a compose is stopping spacing and printing the following characters in the same place. So even if your font have no è it would be created from e and `. They are still two characters in the same space.

A deadkey is somthing else: you type the deadkey "`" and see nothing. but a following "e" will be replaced by an unicode char "è" which is one character (and not two in the same space).

A deadkey will only work with combinations which will result in unicode chars, while compose work with all keycombinations (in theory, it depends of the OS and aplication)

There are combinations of both methods (a compose with a valid unicode result automaticly converted in Unicode), so you compose C= results in a real € char and not simply printed C and = in the same place.

Composing the alphabetic char gets first, then the modification follows. Using Deadkey the modificatin (deadkey) gets first, then the alphabetic char.

For example in windows:
deadkey "`" and "e" (Unicode U+0060 and U+0065) will result in "è" (unicode character 00E8)

e +0300 <ALT> will be get the same optic, but two chars (Unicode U+0065 and U+0300)

Of course real unicode is the more stringent method. But compose is more flexible:

deadkey "" and "w" (Unicode U+0060 and U+0077) will result in "w" (no unicode character availible), you dont get a composition

w +0300 <ALT> will be get the the ` over the w as composition an not unicode char, so it works (if its usefull is another question)

A keyboard-layout with deadkeys can be programmed with free microsoft keyboard layout converter, so you can remap deadkey functions to layers (for example, the AltGr layer is allmost empty, you can map deadkeys there), a goot help for the needed definitions is the greek keyboard layout.
Compose keys can also be mapped, but dont click deadkey in the definition but simply type the unicode of the valid composekeys (beginning at U+0300)

The hard thing will be compose and deadkeys on a WindowsPC with restricted user rights (in office), where you can´t make driver changes and start own programms.

For this you can use an programmable keyboard (for example POS-keyboards) or an microcontroller converter (Soarer-Converter with teensy ++2.0). There you can put the composable chars in Unicode in extra layers.
A way to make real deadkeys in hardware is not easy done - you have to programm your own adapter, a nobody has done it now (but Soarer is thinking about developing his converter for it)