Xdiagnose

GUI tools for diagnosing, repairing, and failsafing X.org issues.

Glxinfo

glxinfo is a command-line tool that can help you diagnose problems with your 3D acceleration setup.

ARandR is designed to provide a simple visual front end for XRandR.

cpuid dumps detailed information about the CPU(s) gathered from the CPUID instruction, and also…

DRIconf is a configuration applet for the Direct Rendering Infrastructure.

feh is an X11 image viewer aimed mostly at console users.

LXRandR is the standard screen manager of LXDE. It manages screen resolution and external monitors.

read-edid is a pair of tools (originally by John Fremlin) for reading the EDID from a monitor.