What is this thing installed on the side?

This think on the side is bothering the crap out of me and I want to get rid of it. I try opening DevonThink preferences and it crashes.

That “thing” is the Sorter (discussed in the Help and manual). It can be turned off in DEVONthink’s Preferences, or more easily Tools > Hide Sorter. If DEVONthink is crashing, hold the Option key in DEVONthink and slect Help > Report Bug.