The Security-Constrained Unit Commitment (SCUC) problem is one of the most fundamental and challenging problems in power systems optimization, being solved daily by Independent System Operators (ISOs) to clear the day-ahead electricity markets. The package provides: (i) an extensible and fully-documented JSON-based data specification format for SCUC, developed in collaboration with ISOs, which can help researchers to share data sets across institutions; (ii) a diverse collection of large-scale benchmark instances, collected from the literature, converted into a common data format, and extended using data-driven methods make them more challenging and realistic; (iii) a Julia/JuMP implementation of state-of-the-art Mixed-Integer Linear Programming formulations and solution methods for the problem; and (iv) a suite of automated benchmark scripts to accurately evaluate the performance impact of newly proposed methods. The package is being developed as part of the "IEEE Task Force on Solving Large Scale Optimization Problems in Electricity Market and Power System Application".