From FBSD_tips

[edit] Admin peeking and poking at things

X11 has been around for a while .... a really long while n fact. Even as it has been extended to an amazing extent, it has still retained backwards compatibility in it's foundations, the tools and utilities that were in use to query the server and window properties are still the same. Sometimes it can pay off to be familiar with these basic utilities, to peek underneath the modern polished exterior of a contemporary X11 desktop.

• xdpyinfo
• xwininfo
• xlsclients
• xprop
• xset
• xkill

[edit] General wizardry

• Desktop multimedia capture with X11