The AGORA Collaboration, primarily led by Ji-hoon Kim, aims to compare various computational astrophysics simulation code in several different tests. In our second paper (arXiv), we use the isolated disk galaxy as a test bed, comparing nine codes. Differences between the final results are small and are more dependent on the input physics instead of the underlying numerical methods. This work verifies the use of past, current, and future galaxy simulations as an accurate tool to understand the astrophysical processes governing star and galaxy formation through cosmic time.