Selectize.js
Optgroups (basic)
Gear:
Select gear...
Pitons
Cams
Nuts
Bolts
Stoppers
Sling
Skis
Skins
Poles
Optgroups (repeated options)
Options:
Select...
Item A
Item B
Item A
Item B
Optgroups (programmatic)
Animal:
Plugin: "optgroup_columns"