SIMBL Agent: Why is it in the login items settings?

Uninstall "SIMBL" or "EasySIMBL" as follows. Back up all data before making any changes.

Triple-click anywhere in the line below on this page to select it, then copy the text to the Clipboard by pressing the key combination command-C:

/Library

In the Finder, select

Go ▹ Go to Folder...

from the menu bar, paste into the box that opens by pressing command-V, then press return. A folder will open. From that folder, delete the items listed below (some may be absent.) You may be prompted for your administrator login password.

Application Support/SIMBL

InputManagers/SIMBL

LaunchAgents/net.culater.SIMBL.Agent.plist

LaunchAgents/net.infinite-labs.SIMBLEnablerForSandboxedApps.plist

ScriptingAdditions/EasySIMBL.osax

ScriptingAdditions/SIMBL.osax

Log out and log back in. There may also be an item named "EasySIMBL" in the Applications folder. Delete it, if so.

Make sure you never reinstall any variant of SIMBL. It’s likely to come bundled with another third-party system modfication that depends on it. If you want trouble-free computing, avoid software that makes miraculous changes to other software, especially built-in applications. The only real exception to that rule is Safari extensions, which are mostly safe, and are easy to get rid of when they don’t work. SIMBL and its dependents are not Safari extensions.

I don't know what you have installed on your computer. Only you know that, so you need to find out. I cannot. Something you installed is responsible for installing SIMBL. If it helps: SIMBL - Wikipedia, the free encyclopedia.

You have installed SIMBL or a third-party utility that uses SIMBL. I would not remove anything until you know what it's for.