Yes, a third humble bundle. :-)

Probably, it will be available later today, check out these links for purchasing and infos:
http://www.humblebundle.com/

http://twitter.com/humble

http://twitter.com/Wolfire

Is it different from the Humble Bundle #3?

No, I don't think so, it is the same:

http://www.gog.com/en/forum/general/humble_bundle_3

Oh, I was asking because there was already a topic called Humble Bundle #3.

Oh sorry, I didn't noticed the thread. I searched for frozenbyte and didn't found anything new.

Still, it's worth of double advertising.

None of those links are saying anything about a 3rd bundle.

Exactly.

That's not the case for these two:
http://www.youtube.com/watch?v=ZaM6LHC_uXA

http://twitter.com/humble/status/57733473024217088

How did that work? Was it announced in advance or later on and what exactly was that mark?

It was announced part way through the event to try and raise the average amount paid. I believe if you paid more than $7 and change you got both bundles. I had already purchased the bundle when this was announced and had payed more than that so I just got an email saying download links for the first bundle were added to my download page.

I don't know if they will do this again as an incentive or not. I would just pay what you want and if they add in an incentive later to raise the average amount paid, you can always go back and increase the amount you paid to qualify. At least that is how it worked with #2.