This repository has releases: https://github.com/openpetra/openpetra-nightlydevzip/releases
This is the zip file with the nightly snapshot of the OpenPetra code, prepared for a quick start of development.
This means it includes the project and solution files for SharpDevelop and VisualStudio, and the binaries, and the Developers Assistant.
It also comes with a sqlite database filled with demo data.
For more details, see the wiki: https://wiki.openpetra.org/index.php?title=Quick_Setup_of_Development_environment