to differentiate in-character from personal posting. The opening message or post of each scene typically lays down the scenario and describes a scene, or continues from a previously started scene. Threads then become an ongoing story in which players periodically advance the plot by reading the latest reply and then responding with what their character does and how the environment changes in response. These replies are often open-ended so that other players can continue. Mediums Message-board role-playing Internet forums (aka Play-By-Message-Board or PBMB, Forum Role-Playing or simply Forum-Games) are the most common medium for Play-by-Post gaming. Forums may provide features such as online dice rolling, maps, character profiling and game history. Using a forum (as opposed to a live-chat interface) allows players to re-read what they have previously written at a later date, and to read posts made by players in other threads. Many online services provide free game hosting specifically for gamemasters, or provide general forum services that can be used for role-playing purposes (such as Proboards or Invisionfree). As an asynchronous collaborative editing tool, forums lack safeguards to prevent two writers from posting simultaneously and contradicting each other. House Rules may require players to take turns sequentially in order to avoid such conflicts, or players may require posts to be edited or deleted to rectify the situation which may result in dispute and intervention from a moderator if one is available. To avoid this, many boards offer guides and tips on roleplay etiquette. Many message boards are listed in roleplay directories, such as TopRPsites to make them easy to find. Twitter and Tumblr are also very popular mediums for Roleplaying. Play-by-post role-playing Play-by-post role-playing is generally devoted to advancing a single overarching storyline that all board members participate in, rather than many different non-related stories proceeding in separate threads [the latter being known as "multi-genre"]. They vary in organization, but the primary formation includes a full set of rules governing role-playing, out-of-character conduct, combat between players, threads detailing a set storyline (often contributed to by plot-advancing, staff-organized events, or player role-plays), character approval forums, and a full staff with admin(s) and moderators. Larger boards set in a single setting are often organized by cutting up the setting into separate forums, each based on locations within the setting. Many message board based games, such as NationStates, establish a hierarchy of moderators to manage plot, pacing and continuity. To keep