The code is hosted at Gitorious. You can obtain your local copy by running following command:
$ git clone git://gitorious.org/trojita/trojita.git
Alternatively, if you don't feel like working with git, you can download this archive with the latest revision of the master branch.
If you prefer to work with something more official, you can try the latest release, 0.2.9.4 -- download it from SourceForge (GPG signature).
Go to the directory created by Git (or unpacked from the archive) and run:
$ qmake CONFIG+=debug ../trojita.pro
$ make -j4
After successful compilation, you can run Trojitá from the build directory:
$ ./src/Gui/trojita
If you encounter a bug in Trojitá, please report it to it's issue tracker. Wishlist items belong to the same place.
Trojitá's IRC channel #trojita (connect from browser) is hosted on Freenode network. The main author, jkt, is often there.
There's a mailing list at trojita@lists.flaska.net, archived by GMane. To subscribe, write a mail to trojita+subscribe@lists.flaska.net, posts from addresses which are not subscribed have to wait for moderation. The issue tracker or the mailing list is the preferred way for reporting bugs and requesting features, while the IRC channel works well for general questions. You can also of course mail the author directly.
If you happen to like Trojita and would like to express your liking in cash, the project accepts donations over SourceForge/PayPal.