U+2E2E

REVERSED QUESTION MARK - the “irony mark” to express irony/sarcasm. A useful character⸮

U+D800

to U+DFFF - surrogate code points. They are only reserved to ease UTF-16 encoding.

U+FEFF

ZERO WIDTH NO-BREAK SPACE - it’s name suggests, that it can be used like U+2060 WORD JOINER. And in fact the latter was introduced to inherit its semantics. This is because U+FEFF had become a special beacon called the byte order mark, that was placed on the beginning of some UTF-8 files. In…

U+FFFD

REPLACEMENT CHARACTER - when a character cannot be displayed (e.g., decoding an erroneous UTF-8 sequency), this code point steps into the breach.

U+1D455

is missing. It would be an italic small “h”. It was not encoded, because it would be identical to the Planck constant ℎ (U+210E).

U+FF03

FULLWIDTH NUMBER SIGN - it is the "Japanese Hashtag" ＃. Sites like Twitter accept it as equivalent to the regular # (U+0023).

U+202D

and U+202E - change the text direction. Relevant XKCD:

U+FE0E

VARIATION SELECTOR-15 - force black-&-white emoji. If this code point follows an emoji, an explicit monochrome rendering of the emoji is requested (if the client supports it).

U+FE0F

VARIATION SELECTOR-16 - force colorful emoji. If this code point follows an emoji, an explicit colorful rendering of the emoji is requested (if the client supports it).

U+00A0

NO-BREAK SPACE - force adjacent characters to stick together. Well known as   in HTML.

U+00AD

SOFT HYPHEN - (in HTML: ­) like ZERO WIDTH SPACE, but show a hyphen if (and only if) a break occurs.

U+200B

ZERO WIDTH SPACE - the inverse to U+00A0: create no space, but allow word breaking.

U+200D

ZERO WIDTH JOINER - force adjacent characters to be joined together (e.g., arabic characters or supported emoji). Apple uses this to compose some emoji like different families.

U+2060

WORD JOINER - the same as U+00A0, but completely invisible. Good for writing @font-face on Twitter.

U+0000

<control> - first code point.

U+10FFFF

(non-character) - last code point. The whole rest of its plane apart from U+10FFFE, the code points in the 0x100000-0x10FFFD range, are private use characters, guaranteed to be never filled by a future Unicode standard.

U+1F402

OX - shortest name.

U+FDFA

ARABIC LIGATURE SALLALLAHOU ALAYHE WASALLAM - longest decomposition form: 18 characters.

U+5146

and U+16B61 - code points that represent the highest “single-digit” number. In both cases that’s 1,000,000,000,000, a trillion.

U+0F33

TIBETAN DIGIT HALF ZERO - code point that represents the lowest “single-digit” number and at the same time the only negative one, -½.

U+006F

LATIN SMALL LETTER O - leads the list of characters with confusable shapes. Of all the possible mappings in the list of confusable characters, the small “o” leads with a whopping 73 entries of similar looking glyphs, followed by U+006C LATIN SMALL LETTER L with 70 entries.

U+1F4C0

DVD - only code point name without any vowel (source)

U+3106C

CJK UNIFIED IDEOGRAPH 3106C - the character with the most strokes: 84. Take your time to write this one!

U+1680

OGHAM SPACE MARK - a space that looks like a dash. Great to bring programmers close to madness: 1 + 2 === 3.

U+037E

GREEK QUESTION MARK - a look-alike to the semicolon. Also a fun way to annoy developers.

U+1DD2

COMBINING US ABOVE - this is the most romantic code point.

U+F8FF

PRIVATE USE CODEPOINT - this private use code point is rendered as Apple logo on many Apple devices.

U+1F574

MAN IN BUSINESS SUIT LEVITATING - A rather curious character, that only made it into Unicode for its appearance in the Webdings font (for reasons of backwards compatibility).

U+1F596

RAISED HAND WITH PART BETWEEN MIDDLE AND RING FINGERS - the Vulcan salute. Live long and prosper! 🖖

U+1F918

SIGN OF THE HORNS - Rock on! 🤘

U+2800

BRAILLE PATTERN BLANK - A Braille pattern that has zero of its six or eight dots filled in. According to the standard: “* while this character is imaged as a fixed-width blank in many fonts, it does not act as a space” Essentially it is rendered as white-space, but since it is designated as not…

Chess figures

.

Card suits

and even a whole deck of cards complete with joker and back of card.

Die faces

and a nice die emoji.

Go pieces

.

Draughts (or checkers) pieces

.

Shogi pieces

, a Japanese variant of chess.

Domino tiles

Mahjong tiles

Cross-platform terminal characters

a list of characters that work on most terminals.