Forge! Huah! What is it good for? More than you might think. Halo 5: Forge has arrived free on Windows 10 and while it's not full Halo 5 with the FPS's campaign and all its multiplayer jazz and whatnot, it's more than the level editor it initially seems. I mean, yes, it does have a level editor, but also it also supports 16-player online Halo action with the Arena multiplayer mode and player-made modes and minigames. Forge is a bit like a basic Garry's Mod, and that's no bad thing for a freebie.
So! Forge has a sandbox where you can slap down and piece together objects to build levels and fiddle with game logic using scripts. Creations are shared across the Windows 10 and Xbone versions, and played online by up to 16 people. Forge is also packing Halo 5's Arena multiplayer mode with its maps. Here, have a gander:
What Forge doesn't have is matchmaking. You'll need to play through custom game lobbies, which makes it all fiddlier and a bit of pain to organise if you're not playing with pals. You can't find or join games that are already going either; that'll come in a future update.
Now that Microsoft are bringing their big Xbone games to Windows 10 too, presumably the next Actual Proper Halo will come round our way too. I believe the whole thing's about a surly uncle babysitting a sexy computer? The last Actual Proper Halo we got was Halo 2, though the (recently-cancelled) free-to-play Halo Online intended for Russia has been opened up and expanded by modders.
Remember how Microsoft originally called this Forge – Halo 5: Guardians Edition? What silly sausages!