[gourou]

Nothings beats a white board for explaining something

[brightfog]

Yes true but a missing whiteboard often leads to well executed specs and mockups.

[gourou]

What interactive online tool are you using to explain/come up with a solution to an issue?

[brightfog]

There isn't any dedicated interactive online tool for explaining I am aware of.

The most powerful tool for collaboration and communication though is screen-sharing + your mouse cursor + your voice available in any video calling software.