I try to create an ad-hoc network between many Android devices, but I can\'t find documentation to do that.
I thought Wifi direct could work for what I want, but is
The Serval Project, based in part on WiFi Tether, is the only place I've found this functionality. It's still alpha phase, but seems to be the forerunner in the field. The wiki is much more useful than the main project page linked above, with installation instructions and a bit of documentation.
Serval may or may not be right for your needs, but I felt it should be pointed out that ad-hoc networking is not impossible on Android. It might be better to wait until Google gets around to implementing it as standard API, though (if you believe they ever will :) ).