The Team Fortress 2 blog announces that the Team Fortress 2 patch mentioned this morning includes a community-created Invasion event. This page has the details and this trailer showing off what this is all about, and here's word:

The TF2 team is proud to announce Invasion, a wholly community-created update featuring an animated short, 16 new cosmetic items, reskinned weapons with cool death effects, a taunt, four maps, Unusual particle effects, and even an update landing page. It represents a boatload of work from some incredibly talented members of the TF2 community. Buy your Invasion Community Update Pass today!