Is there a command or tool in Sonar Platinum to prevent MIDI notes from overlapping? Here's a before-and-after of what I'm talking about:

 
Not looking for machine-like precision, but selecting a few notes and making them legato would be nice.

There's an included CAL script  (Process > Run CAL) called SiNGLE.CAL that does this - eliminates overlaps without lengthening notes to make them legato like LEGATO.CAL. But I found it had issues with short grace notes so I wrote my own some years ago using different logic.
 
I can't guarantee mine won't get tripped up by some unanticipated input, either, but if you PM me your e-mail address, I can send you a copy.

brundlefly
There's an included CAL script  (Process > Run CAL) called SiNGLE.CAL that does this - eliminates overlaps without lengthening notes to make them legato like LEGATO.CAL. 

 
The only caution I learned after picking up a lot, is that using SINGLE.CAL or LEGATO.CAL, all selected notes should be INSIDE A THE SAME CLIP, otherwise they will not work properly.

Therefore, to ensure, before using any of these scripts, always make a bounce for all notes remain in a single clip.
 

Lemme see if I understand...
 
Say, I have a MIDI track that's 5 minutes long. Inside, there are several clumps of notes that overlap. I should cut those sections (CTRL-S) before applying the script? Otherwise, the entire track gets treated? (I'm cooking and baking at the moment, or else I'd just try it and see.)
 
Back to the kitchen...
 
EDIT: I lassoed a string of notes and ran LEGATO.CAL. Worked perfect! Thanks, all.