|Editor OS||Windows, OS X|
|Publish on||Windows and OS X desktop and webplayer, IOS, Android, NaCl, BlackBerry, Windows 8 (store and phone), XBOX 360, PS3, Wii|
Unity3D is the default choice for indie developer and not only to them. Big studios like Blizzard using it for games like Hearthstone: Heroes of Warcraft, have been seduced by the easiness of prototyping and the accelerated workflow.
The key strength of Unity is the easiness of starting a project. One can make assemble a basic game in a matter of hours. Importing assets in Unity is as easy as dropping them in the project folder, as long as you use popular formats like .fbx for 3D models or .psd for 2D. But Unity allows the conversion of Blender files too and this makes it great for budget constrained indies who can't afford to spend thousands of euros on professional tools like Maya or 3D Max.
Unity can export to a large variety of platforms. Among the first ones were OS X and Windows desktops (actually the engine started as being exclusive to Mac world, then they exported the game to Windows and after this the big opening to Windows world with the windows editor version) then iPhone, Android, NaCl (Google Chrome native client), XBOX 360, PS3, Wii, Linux, BlackBerry, Windows 8. At some point they had an flash exporter too, but development for this had been stopped and no more licenses are sold.
Another thing worth mentioning is the free version (as in free to make games and sell them without being required to give anything back). The free version attracted a huge number of people interested in making games.
Unity is an all pupose engine, meaning you are not constraint to a specific genre. This versatility comes with a cost and requires a fair amount of knowledge to finish up a AAA game.Luckily for many beginners there are a phew ways to get around this: the community, the asset store and the knowledge base found on internet, which increase by the minute. If you are a complete newbie in the game development, not only you can find extremely good tutorials on the official website but there are many blogs scattered around the world wide web giving answers and even scripts and complete projects. Worth here to mention video tutorials on YouTube and especially those produced by BurgZergArcade.
On the price side, Unity can be very pricy, especially if you want to publish on all platforms he is capable to export: a pro version with exports to desktops and free version for mobile is $1500 and then $1500 for each of following: IOS, Android, Blackberry and $500 for Team License. These prices are all for one user and while you can install the same license on one or more computers (desktop and laptop usually) it is permitted to use the same license for more developers. Also another restriction is the fact that you cannot mix free licenses and pro licenses in a firm.
When I said Unity didnt care how much money you make with your game, this is not entirely true. There are two limitations as far as I know: first is for free version, if you exceed $100,000 in revenues you are required to buy the Pro license. The second one come in place when developing gambling games, where you need to get a separate deal from Unity.