I used Haddock server (https://wenmr.science.uu.nl/) to perform protein protein docking and compare it to other web tools it provided me with the least RMSDs.
The ZDOCK program (http://zdock.umassmed.edu/) is mainly used to search for all possible binding patterns obtained by translation and rotation between two proteins, and evaluate each binding pattern using an energy-based scoring function model.
SwissDock (http://www.swissdock.ch/) is a free online molecular docking tool used for simulating protein-small molecule interactions.