Split notes by drawing a line with the mouse:
* Intended to mimic the functionality of FL Studio's Slice Tool.
Available in ReaPack, or direct download links:
js_Split selected notes by drawing a line with the mouse
js_Split notes by drawing a line with the mouse
[EDIT: There is useful discussion regarding this script in the original Feature Request thread:
diagonal line split - midi notes.]
EDIT 2016-07-08: The new Trim notes script works similarly: