1. An online system of conducting a contest and determining one or more winners of the contest through a progressive cascade of elimination competitions, the system having a backend server configured to conduct two-way communication with a plurality of client computing devices each operated by a respective participant user of a plurality of participant users each registered to the online system for participating contests conducted by the online system, the backend server having at least one processor, one memory, and one networking interface device configured to conduct two-way communication with the plurality of client computing devices, the backend server having access to at least one database configured to store contest aggregate data aggregated and configured to run the contest, each respective client computing device having at least one processor, one memory and one network interface device configured to conduct two-way communication with the backend server, the progressive cascade comprising a plurality of cascade levels each having one or more contest rooms each having a respective group of contestant users and holding, among the respective group of contestant users, a respective elimination competition used to progress the contest, the plurality of cascade levels including a lowest cascade level, a highest cascade level, and zero or more intermediate cascade levels, the system comprising: a cascade-starting means configured to programmatically create the lowest cascade level and form one or more respective contest rooms at the lowest cascade level; a contest-room-joining means configured to enable a respective participant user from among the plurality of participant users to select and join a respective contest room at the lowest level of the plurality of cascade levels so that the participant user becomes one respective contestant user of the group of contestant users of the selected respective contest room; a contest-room means configured to programmatically emulate each of at least one contest room at each of at least one cascade level of the plurality of cascade levels, the contest-room means configured to hold, for each of at least one contest room at each of at least one cascade level of the plurality of cascade levels, the respective elimination competition among the respective group of contestant users, the contest-room means configured to enable, for each respective contest room, each contestant user of the respective group of contestant users to upload, from one or more respective client computing devices of the respective contestant user to the backend server, a respective set of competition input data of the respective contestant user configured to enable the respective contestant user to compete in the respective elimination competition; a contest-room-winner-subgroup-deciding means configured, for each of at least one contest room at each of at least one cascade level of the plurality of cascade levels, to programmatically decide, from among the respective group of contestant users, a winner subgroup of one or more contestant users as winning the respective elimination competition based on a collection of the uploaded respective sets of competition input data of the respective group of contestant users; a cascade-progressing means configured to progress the contest from a current cascade level of the plurality of cascade levels to a next higher cascade level of the plurality of cascade levels, the cascade-progressing means configured to create the next higher cascade level and form one or more respective contest rooms at the next higher cascade level, the cascade-progressing means configured to fill in each of the respective one or more contest rooms formed at the next higher cascade level with the respective one or more winner subgroups of contestant users each winning one respective contest room of the one or more respective contest rooms formed at the current cascade level; a cascade-concluding means configured to conclude the contest at the highest cascade level based on one or more winner subgroups of contestant users each decided as winning a respective contest room formed at the highest cascade level; and a real-time-contest-room-synchronizing means configured to cause, for each of at least one contest room at each of at least one cascade level of the plurality of cascade levels, one respective client computing device operated by a respective contestant user from among the respective group of contestant users, to be synchronized with the respective elimination competition in real-time and display on the respective client computing device a first user interface indicative of a real-time state of the respective elimination competition.