rust is an open world pvp survival game, you spawn in the world with low materials but the ability to gather, you gather, you craft items to help you survive like walls doors and eventually entire buildings. but the main focus is on survival insofar as you need to constantly gain resources for hunger, comfort and protection. protection being split into two categories, the elements, and other players.
you can gather from items that spawn in the world, and from trees and animals, or you can raid other players and their homes. you may choose you’re style of acquisition. but if you do not do one, you will die. sometimes you will have no choice and be forced into one or the other situation.
as you progress over time, you will learn to craft more complicated items, but also require skill to protect your creations. and cunning to hide them.
you can store items in boxes, but they can be looted by other players. if you die you drop whatever you are carrying. any crafting recipes you have learned persist after death, currently.
currently it runs on the unity engine, and runs from a browser, just personal conjecture, i think its because its easier to update and have the user base readily keep the same version, but it would not be difficult to create a standalone product at completion. no release dates or open access dates are yet given. they have milestones they are trying to achieve in some months, but the exact scope and time of these are still vague. they will probably stay vague until they can be assured they can make the date.