Easily clone and/or reverse selected keyframes across multiple properties or layers in After Effects! No more hoping you can paste multiple keyframes without getting duplicated effects or layers. And on the off-chance it does work, time-reversing those keyframes only to have to retime those keys anyway. Key Cloner is a pay-what-you-want tool. Thanks for any support you can give.
$0+ Get it now! Compatibility: After Effects CC (12.2)+
Untested with earlier versions

Key Cloner is a ScriptUI panel that has simple buttons:

Clone Keyframes

Copies the selected keyframes to the current time, even across multiple properties or layers!

Clone + Reverse

Clones the selected keyframes and mirrors their arrangement, keeping their relative timing!

Reverse Keyframes

Time-Reverse Keyframes, but the right way. Reverses the order of the selected keyframes keeping their relative timing, but does not move them to the current time, leaving them in place.

Move Keyframes (unpictured)

This one’s pretty simple: it moves the selected keyframes to the current time. Sometimes dragging the keyframes around isn’t as convenient as hitting a button.

KBar Support

Key Cloner also works with KBar so you can use Key Cloner without a separate script panel. Create a script button and point it to KeyCloner.jsxbin. Use one of the following in the “Script functions or arguments” field:   
clone

reverse

clone reverse

move

last (added to any command except ‘reverse’, e.g. ‘movelast’)
Use the included SVG icons, change them, or create your own!

Keyboard Shortcuts

This one’s hacky, but it works! By copying the script file to the Scripts folder and adding some extra text, you can assign those script to shortcut with AE’s Keyboard Shortcut Editor. See the readme for more details. Happy Keyframing!