Optimal Two-Stage Designs for Ordered Categorical Outcomes R package OptOTrials version 1.0.2 Functions to design and simulate optimal two-stage randomized controlled trials (RCTs) with ordered categorical outcomes, supporting rank-based tests and group-sequential decision rules. Methods build on classical and modern rank tests and two-stage/Group-Sequential designs, e.g., Park (2025) <doi: 10.1371/journal.pone.0318211>. Please see the package reference manual and vignettes for details. Software Depends: R (>= 4.0) Imports: stats Yeonhee Park <yeonheepark@skku.edu> Comprehensive R Archive Network (CRAN) Yeonhee Park [aut, cre], Yudi Wang [aut], Zhanpeng Xu [aut] GPL-3 2025-09-05 application/tgz https://CRAN.R-project.org/package=OptOTrials doi:10.32614/CRAN.package.OptOTrials