A GM sim is a sports management game in which you make a team's front-office decisions (drafting, trading, signing and paying players, setting the lineup) and a simulation engine plays the games. The genre is also called a basketball GM game, a franchise sim or a text sim.
HoopSim is a free, browser-based basketball general manager simulation game. You run a pro basketball team: draft, trade, sign free agents under a real salary cap, and set the depth chart and game plan while every possession is simulated. Play solo or in multiplayer leagues with friends, a commissioner and AI-run GMs that negotiate trades in chat. What separates GM sims from fantasy sports is that the games are simulated rather than scored from real ones, and what separates them from console franchise modes is that nobody holds a controller: a season is decisions, box scores and consequences.
Rulebook: How to Play. Related: sim league, AI GM, commissioner.