Looks like you've still got time to send in your maps and skins for possible inclusion in the upcoming Starsiege: TRIBES Extreme. The following was just posted to TRIBESPlayers:

We've been getting more and more maps and skins in the last few days. The deadline will be pushed back so that those just now finishing up can take the extra time to polish everything. The amount that we have coming in right now really shows that many are taking every bit of time to make their entries the best they can be. I wouldn't want to lose any or have someone slight their work because of some stupid date... So the Open call Date will be extended to Sept 17th!

If you're interested in entering, swing by the contest page for full details.