Any Facebook apps that does this?

[MaRsBarS]

Is there any application on Facebook I can use to tell who is online when your appearing offline???

[Tasha]

Nope

[Mason L]

Well if you make people think you are offline and want to know who is online you can just use the chat thing at the bottom right corner.

[scribbledouttx]

Try the facebook chat which is located on the bottom right of the screen. It will let you know who is on facebook at the time and who is idle. Hope this helps.