Destiny 2 Faction Rallies are restricted to players who have reached level 20 and finished the campaign, so if you're not there yet and have no idea what "factions" are, don't sweat it—go finish the game and then come on back when you're done. (Don't feel a need to rush, though, these are repeating events.) For everyone else, since the new one announced yesterday will be the first Faction Rally that PC players can take part in, read on.
(And yes, if you're not eligible yet but curious anyway, you're welcome to come along too.)
Faction Rallies are week-long events that pit the game's three factions—Dead Orbit, Future War Cult, and New Monarchy—against one another in indirect competition. While the rally is live, players who have pledged to a faction will earn tokens by completing various sorts of tasks like public events, looting Lost Sectors, taking part in the Crucible, or running strikes or raids. Those tokens can be turned in to faction vendors for engrams, which will deliver faction-themed legendary armor and weapons, and also cosmetic items. Here are the guns...
The faction that's acquired the most engrams when the rally wraps up is declared the winner, and for one week thereafter its members will have the opportunity to buy the "Winner's Offering" weapon for 1000 Glimmer. Everyone else will be able to buy it too, but it'll cost 50,000 Glimmer. The three possibilities are pictured in the gallery below.
The first Faction Rally ran through the end of September and into October, and was won by Dead Orbit—the "space goths," as Eurogamer described them. The next one will begin on November 7 and run to November 13, and since it will be the first for a lot of us, here are a few links to help you prepare: A detailed rundown of Faction Rallies at bungie.net, and courtesy of Reddit, what you need to know about which Faction is right for you and what you can expect from each of them, and all the Faction weapon drops you can look forward to.