DefaultKeyBinding.dict file (~/Library/KeyBindings/DefaultKeyBinding.dict) for Mac OS X, created by Brett Terpstra and based heavily on work done by Lri. Please note that these bindings won't work in all applications: TextWrangler and TextMate, for example, override these with their own settings.

Installation: Copy the DefaultKeyBinding.dict file to the ~/Library/KeyBindings/ directory (create KeyBindings if it doesn't already exist). Any open applications will need to be re-started before the key bindings will take effect --- or log out and log back in.

The repository includes a script to generate a Dash docset from your customized version of the file. See here for details.

Documentation (last updated 12/21/2023.)

Grouped items begin with the groups shortcut (if exists), followed by a subgroup (if exists) followed by the keys specified.

General Commands
Key	Function
⌃y	Replace yank: command with yankAndSelect for use with the kill ring (defaults write -g NSTextKillRingSize -int 6)
⌃⌥y	Regular yank, only insert last register and don’t select
⌃⇧u	Uppercase word
⌃⌥u	Lowercase word
⌃⌥t	Titlecase word
⌃⌥⇧u	Uppercase current paragraph
⌃⌥⇧t	Titlecase paragraph
⌃w	Delete word before cursor
⌥w	Select word
⌥⇧w	Select word backward and modify selection
⌥⇧s	Select entire line/paragraph
⌥s	Select from beginning of paragraph to last character
⌃⌥⇧s	Select paragraph excluding leading/trailing whitespace (same as ^$@\UF701)
⌥d	Delete line/paragraph
⌃u	Delete to beginning of paragraph (if this isn’t already defined?)
⌥y	Copy paragraph
⌥x	Cut paragraph
⌥p	Paste paragraph below
⌃⌥p	Yank (from kill ring) paragraph below
⌥⇧p	Paste paragraph above
⌃⌥⇧p	Yank (from kill ring) paragraph above
⌃⇧a	Select to beginning of paragraph and copy
⌃⇧e	Select to end of paragraph and copy
⌥q	Cut to beginning of paragraph
⌥k	Cut to end of paragraph
⌥o	Blank line after current
⌥⇧o	Blank line before current
⌃⌘k	Move line up
⌃⌘j	Move line down
⌃⌘l	Indent line
⌃⌘h	Outdent line (one tab or char)
⌃⌘↑	Move line up (same commands but with arrow keys)
⌃⌘↓	Move line down
⌃⌘→	Indent line
⌃⌘←	Outdent line (one tab or char)
⌃⇧⌘←	Full outdent - Deletes all leading space of line/paragraph (updated) (Control-shift-command-left arrow)
⌃⇧⌘→	Delete trailing space (Control-shift-command-right arrow)
⌃⌘⇧↑	Delete leading and trailing whitespace for paragraph (Control-shift-command-up arrow)
⌃⌘⇧↓	Select paragraph without leading or trailing whitespace (Control-shift-command-down arrow)
⌃⌥⇧↑	Modify selection up by paragraph (Control Option Shift Up) (Control-option-shift-up arrow)
⌃⌥⇧↓	Modify selection down by paragraph (Control Option Shift Down) (Control-option-shift-down arrow)
⌃⌥⇧←	Modify selection left by word (Control-option-shift-left arrow)
⌃⌥⇧→	Modify selection right by word (Control-option-shift-right arrow)
⌘⌥⌃←	Move to first Alphanumeric character of line (Control-option-up arrow Control-option-command-left arrow)
⌘⌥←	Move to first non-whitespace character of line (Control-options-left arrow)
⌘⌥⇧←	Select to first word of paragraph modifying selection (Options-shift-command-left arrow)
⌘⌥⇧→	Select to end of paragraph modifying selection (Option-shift-command-right arrow)
⌥⌘→	Move to last non-whitespace character of paragraph (Option-command-right arrow)
⌃⌥→	Move to end of paragraph and delete trailing whitespace (Control-option-right arrow)
⌘↩	TextMate Command-Return (Command Return)
⌘⇧↩	Insert blank line above paragraph (Command Shift Return)
⇧⌥␣	Insert space and uppercase next character (Shift-Option-Space)
⌃⇧␣	Uppercase next character (Control-Shift-Space)
⌃⌥␣	Move cursor forward with spacebar (shift-space)
⌘⌥_	Hyphenate next space and move to next word (this will kill non alphanumeric symbols and punctuation, use only on words)
⌥1	Bookmark
⌥2	Jump to bookmark
⌥⌘↩	Continue a list item with indentation and include the same delimiter (Command Option Return)
⇧⇥	Remove one tab (or character) from start of line (outdent) (Shift Tab)
⌘⌥b	Bold selection (Markdown)
⌘⌥i	Italicize selection (Markdown)
⌘⌥`	Backtick selection (Markdown)
⌃⌘↩	Break line with double space (Markdown) (Control-Command-Return)
⌘⌥=	Increase markdown header level
⌘⌥-	Decrease markdown header level
⌘⌥>	Increase blockquote header level
⌘⌥<	Decrease blockquote level
⌃<	Make selected text into paired HTML tag. Allows attributes, only dupes first word into closing tag (caveat: overwrites your pasteboard)
⌥⇧r	Repeat character before cursor
⌘⇧⌦	Forward delete to end of paragraph
⌘⇧⌫	Delete to beginning of paragraph (Command-shift-delete)
⌘⌥7	Right mouse click (useless, doesn’t maintain cursor position)
⌘⌥⇧s	Real, honest-to-goodnes Save As…

Multi–stroke casing commands (⌃⌥c)
⌃⌥c		c	Snake_case to camelCase (delete forward and capitalize)
⌃⌥c		s	Snake_case word break

Commenting commands (⌃⌘c)
⌃⌘c		/	Comment with “//”
⌃⌘c			Comment with “#”
⌃⌘c		!	HTML commenting
⌃⌘c		*	Css Commenting

Multi–stroke Markdown commands (⌃⌘w)
⌃⌘w		␍	Force carriage return in text field
⌃⌘w		⇥	Force tab in text field
⌃⌘w		[	Insert reference link [selection][[cursor]]
⌃⌘w		]	Insert reference [selection]: [cursor]
⌃⌘w		`	Fence code (new) (Requires text selection)
⌃⌘w		f	Insert inline footnote marker or inline footnote (new)
⌃⌘w		+	Unordered list item with +
⌃⌘w		-	Unordered list item with -
⌃⌘w		*	Unordered list item with *
⌃⌘w		.	Numeric list item (new)
⌃⌘w		8	Convert current numbered list item to bullet, handles indentation
⌃⌘w		1	Convert current bullet list item to numbered
Headlines (removes leading whitespace after inserting hashmarks) (h)
⌃⌘w	h	1	#
⌃⌘w	h	2	##
⌃⌘w	h	3	###
⌃⌘w	h	4	####
⌃⌘w	h	5	#####
⌃⌘w	h	6	######
Markdown link (l)
⌃⌘w	l	t	Create a link for selected text, cursor between () [selected text]([cursor]) (links without selected text first, these can produce a mess using multiple clipboards make a text selection before you run them)
⌃⌘w	l	c	Create a link for selected text, inserting clipboard as url [[cursor]selected text](clipboard contents)
⌃⌘w		s	SearchLink Basic Link
Link as image (i)
⌃⌘w	i	t	Same as lt, but with image syntax \!\[selected text]([cursor])
⌃⌘w	i	c	Same as lc, but with image syntax \!\[selected text](clipboard)
⌃⌘w	i	d	Same as lc, but with image syntax and “+” for Droplr links 
Reference links (:)
⌃⌘w	:	t	Create a reference from selected text
⌃⌘w	:	c	Create a reference from selected text, clipboard as url

HTML commands (⌃⌘e)
⌃⌘e		=	=“[cursor]”
⌃⌘e		e	Entity &[cursor];
⌃⌘e		/	Https://
⌃⌘e		t	Make previous word into paired HTML tag
HTML Links (a)
⌃⌘e	a	t	Insert HTML link for selected text, leave cursor in the href with “https://” selected
⌃⌘e	a	c	Insert HTML link with clipboard as href
HTML Image (i)
⌃⌘e	i	t	Insert image tag, any selected text is alt text, leave cursor in src attribute
⌃⌘e	i	c	Insert image tag, clipboard as src, any selected text as alt, leave cursor at beginning of alt attribute

Surround commands (⌃⌘s)
⌃⌘s		(	Wrap () no spaces
⌃⌘s		)	Wrap () with spaces
⌃⌘s		[	Wrap [] no spaces
⌃⌘s		]	Wrap [] with spaces
⌃⌘s		{	Wrap {} no spaces
⌃⌘s		}	Wrap {} with spaces
⌃⌘s		<	Wrap <> no spaces
⌃⌘s		>	Wrap <> with spaces
⌃⌘s		'	Wrap single quotes
⌃⌘s		`	Wrap backticks

Jekyll Shortcuts (⌃⌘j)
⌃⌘j		p	Pullquote Liquid Tag (new)
⌃⌘j		r	Raw Liquid Tag (new)
⌃⌘j		⇧r	Raw Tag for entire paragraph (new)

TaskPaper Tags (⌃⌘t)
⌃⌘t		d	@done (new)
⌃⌘t		p	// @priority() (new)
⌃⌘t		n	@na (new)
⌃⌘t		t	@today (new)

SearchLink commands (⌃⌘g)
⌃⌘g		g	SearchLink Syntax: Google (new)
⌃⌘g		⇧a	SearchLink Syntax: Amazon (new)
Apple (a)
⌃⌘g	a	i	SearchLink Syntax: iOS App (new)
⌃⌘g	a	m	SearchLink Syntax: Mac App Store (new)
⌃⌘g		s	SearchLink Syntax: Software (new)
⌃⌘g		m	SearchLink Syntax: IMDB (new)
⌃⌘g		b	SearchLink Syntax: BrettTerpstra.com (new)
⌃⌘g		p	SearchLink Syntax: BrettTerpstra.com Projects (new)
⌃⌘g		t	SearchLink Syntax: Twitter User (new)

This documentation is generated automatically from the comments and commands in the DefaultKeyBinding.dict file. The script document_keybindings.rb is free for use, but it's specifically designed for use with my formatting in the bindings plist (i.e. it's a little finicky).