By George, I believe you've got it!
KeyFinder produces a complete grid of any font's character set (16 rows x 16 columns = 256 characters).
Clicking on any cell produces the keystroke combination to produce that character in a text. So, eg, the euro sign in Chicago is created by opt+shift+2; apple symbol is opt+shift+K.
That's why it's a gem.
Uh, 265 characters is hardly all
the characters in a font.
For that matter, fonts don't contain characters
, they contain glyphs
. Back in the bad old days (and I mean, really really bad), we were limited to only 8-bit representations of characters, and thus there were only 256 characters total. We got around that by using different fonts, so that we could get different glyphs for the same character. Thus, the character with code 97 (or 0x61 if you prefer hexadecimal notation for your numbers), would have a glyph that looked like a lower-case letter 'a' in a "U.S." font, but would look like a lower-case letter 'alpha' in a "Greek" font.
One problem is that, despite appearances, it was still the same character 97. Change your font (or ship your document to someone who didn't have your fonts installed), and your text appeared to change languages.
Another problem is that if you searched for a string containing an 'alpha' character, you'd find all the strings containing an 'a' character as well, because the search would actually be for strings containing "character 97", regardless of what it might look like.
And one side effect is that people would utter phrases like "type such-and-so to get ... in the Chicago font", just like you did above. The nearest correct phrasing is "type such-and-so to get character number ..., which in Chicago looks like ...".
Enter Unicode. We now have over a million characters, not a paltry 256, to play with. Each character has its own code (and its own official name). Thus character 97 (0x61) is LATIN SMALL LETTER A, and character 945 (0x03B1) is GREEK SMALL LETTER ALPHA. Changing fonts may make the glyph slightly different, for example by making it bold and/or italic, or changing the line thickness or serifs, but an 'alpha' will always be an 'alpha', never an 'a'.
Some fonts, especially the Asian ones, have thousands of glyphs in them. There's no way a teensy 16x16 grid could possibly list them all.
And yet, even Unicode still has vestiges of the old way of thinking. The range of characters from 0xE000 thru 0xF8FF is set aside as a "Private Use" area. Characters in this range purposely have no official definition, and can look like whatever the font wants them to look like. The last 48 characters of that range, from 0xF8D0 thru 0xF8FF, are considered OS-specific. That is, each operating system decides the meaning of those characters. The last one, at 0xF8FF, is usually given a glyph that represents the OS.
When the Unicode consortium refused to set aside a range of characters for Klingon, the Linux community responded by putting the Klingon alphabet in this range, with 0xF8FF being the Klingon Federation Symbol.
On OS X, that same character is the "solid apple" character, the one you get by typing shift-option-K on a U.S. Keyboard. Put that character in a document and send it to someone running Linux, and it'll look like a Klingon Federation Symbol.
Which keyboard you're using will affect what characters you can type and how you type them. Type shift-option-K on a "U.S. Extended" keyboard, and you'll get a RING ABOVE character (730, or 0x02DA).
The way to see all the characters available is with the Character Viewer. To get the Character Viewer, either select Edit → Special Characters... in any application that has that menu item (Finder, for example), or enable "Keyboard & Character Viewer" (In Lion, that's in System Preferences → Language & Text → Input Sources) and select "Character Viewer" from the Input menu (icon looks like a flag).
The way to find out how to type a character is with the Keyboard Viewer. (Enable it in System Preferences, then choose it from the Input menu.) You'll see a picture of your keyboard, and can try various combinations of modifier keys to see what each key will do. Keys that appear orange represent "dead keys"; type one, and nothing appears in your document, but the keyboard gets temporarily re-mapped so you can type otherwise inaccessible characters. "Dead keys" should more properly be called "lead-in keys", because they initiate multiple-key combinations. For example, on a "U.S." keyboard, the dead key option-e temporarily turns the ordinary key 'a' (LATIN SMALL LETTER A) into an 'á' (LATIN SMALL LETTER A WITH ACUTE) key.
Or, find the character in the Character Viewer, and double-click it to type it into the current document.