Ukelele

Ukelele is a Unicode keyboard layout editor for the XML-format keyboard layout files in OS X (".keylayout" files). It provides a graphical interface to the layout files with support for drag-and-drop character assignments, creation of dead keys, and assignment of multi-character strings.

Ukelele is not able to reassign modifier keys (Option, Shift, Command, Control, caps lock), or change the function of special keys (Return, arrow keys, function keys, etc). Rather, it is for creating keyboard layouts for different languages or other needs.

By the way, the name of this software is intentionally misspelled (try pronouncing it "You-KEY-lay-lay"). Call it an instance of 'artistic license'.

Note: Now requires OS X 10.9 or later

• Installing keyboard layouts is changed, bringing the capabilities of the companion application, Keyboard Juggler, into Ukelele as the Organiser window. This should simplify the process of installing and uninstalling, and is designed to avoid certain traps, such as editing an active keyboard layout.
• The installer disk image has been redesigned, with an application for installing the keyboard layout rather than a symbolic link.
• The keyboard window has an information panel to tell some basic things about the current state: dead key state, modifier set, keyboard type and coding.
• Updated to Unicode 11.0 and the latest (2018-10-31) version of the language tag database, so that the language dialog now has the latest names.
• Introduced an option not to use symbols on non-modifier keys.
• There is a more robust system for creating icons when creating a keyboard layout from the current keyboard input source.
• Keys whose code is not known are now labelled as ordinary keys, and so can have output assigned. This is most useful for Japanese keyboards and third-party keyboards with extra keys.
• A rare bug occurred when deleting a dead key state when there were inline actions (meaning that the keyboard layout had been edited by hand, most likely) and then undoing the deletion. This is now fixed.