GLIMMPSE is described in:
Kreidler SM, Muller KE, Grunwald GK, Ringham BM, Coker-Dukowitz ZT, Sakhadeo UR, Barón AE, and Glueck DH (2013) GLIMMPSE: online power computation for linear models with and without a baseline covariate. Journal of Statistical Software, 54(10). PMCID: PMC3882200
Please cite accordingly in your work.