iOS 7.1 has only just launched but already we're itching for iOS 8 and we're not alone, as rumors of what the new version of Apple's OS might include have started circulating.
Enough have dropped for us to start to get an idea of what form iOS 8 might take, so without further ado here's what we've heard so far.

Release date

New versions of iOS tend to get announced at Apple's Worldwide Developers Conference (WWDC) and there's been no suggestion that iOS 8 will break the trend. This year's WWDC 2014 has been confirmed as kicking off on June 2, which is when we anticipate the keynote speech will be.
However, while iOS 8 will likely be announced then it probably won't actually launch until later in the year, making its debut on the iPhone 6. Again, this is all based on Apple's past iOS launches.
Cut to the chase
What is it? The next iteration of Apple's mobile platform
When is it out? Probably sometime in September 2014
What will it cost? iOS 8 will be a free download

Healthbook

Apple, like Samsung, seems to be pushing the health and fitness capabilities of its products and the next step of that is likely to come with iOS 8.
According to unnamed sources who spoke to 9 to 5 Mac, iOS 8 will come with a new app dubbed Healthbook. Supposedly it will have a similar interface to Passbook, but will track steps taken, distance travelled, calories burned and weight loss.
Healthbook
So in other words it's doing the same job as stand alone fitness trackers like the FitBit Force, which makes sense since Apple already built an M7 motion co-processor into the iPhone 5S to track just those sorts of things, so it might as well make the most of it.
However apparently it will also go way beyond that and track hydration levels, blood pressure, heart rate, blood sugar, nutrition information and respiratory rate, taking it a step beyond existing fitness trackers. 9to5mac has even recreated some images of how the app will supposedly look.
Healthbook 2
Obviously no existing Apple hardware has the relevant sensors to track most of that stuff, but there's been talk recently that the iPhone 6 might have an array of new sensors, plus some of it may rely on Apple's unconfirmed iWatch.

Apple Maps

Apple Maps has had a bit of a tough time so far. Its launch was as far from smooth as possible and while it's no longer putting train stations in the middle of the sea it still lags some way behind Google's offering.
That could be about to change though, as 9 to 5 Mac claims to have spoken to "sources briefed on the plans" and learned that public transport directions for trains, subways and buses will be added to Maps, initially for major US cities, with a wider roll out likely to follow.
The same sources also claim that it will be more accurate than it is now and new points of interest and labels will be added for things like stations and airports.
Apple Maps
The appearance of the app has apparently been improved too, making streets more visible. Supposedly Apple is also working on an augmented reality feature, which will allow you to see points of interest on your camera viewfinder, though it's thought that this feature won't make it out in time for iOS 8.
Late last year Apple patented some major new ideas for Maps, which would add a whole new level of interactivity beyond even what's currently rumored.
It would allow users to tap a road for example and see information relevant to just that road, such as any junctions on it, or to tap a restaurant and get a menu.
This functionality might be some way off yet, if it emerges at all, but we live in hope that it might make an appearance in iOS 8.

Siri

Apple could hardly release a new version of iOS without updating everyone's favourite personal assistant.
According to tech site The Information, Apple wants Siri to be able to interface with third party apps. Currently it's compatible with a number of popular third party apps, but only because Apple worked directly with the developers to add the functionality.
Siri
It's rumored that Shazam might be embedded right into the new version of Siri, allowing you to verbally ask Siri what song is currently playing without having to open the Shazam app.
In future any and all app developers might be able to make their apps compatible with Siri without Apple's help, which would vastly increase Siri's usefulness, allowing you for example to use third party messaging apps and calendars to send messages and set reminders.
There's also talk that Siri might be able to contextually launch specific apps in future, so for example if you start jogging it might automatically launch RunKeeper, rather than you having to ask it to.

iTunes Radio and HD audio

Apple looks to be putting more weight behind iTunes Radio, if sources speaking to 9 to 5 Mac are to be believed. The sources claim that it will be given a separate app for iOS 8, as currently it's part of the Music app.
iTunes Radio
Supposedly other than becoming its own app it's going to remain exactly as it is now, which isn't so surprising as it only launched last year, but by giving iTunes Radio its own app it will be more noticeable to users and better positioned to take on other streaming services like Spotify.
Alongside that it's looking like we might get HD audio, with rumors swirling that Apple is preparing the feature for iOS 8. If true it would mean new headphones and lightning cables would be required to make use of it. We can't help but wonder if this ties into the Beats buyout Apple might be working on.

Preview and Text Edit

We recently got our first glimpse of what might be iOS 8. Based on the image it unsurprisingly looks a lot like iOS 7, albeit with a few new apps on board.
There's an icon for the aforementioned Healthbook and one for Tips, which is likely a user guide, but there are also Preview and Text Edit icons.
iOS 8
If those names sound familiar it's because they're existing pieces of software for OS X, but now seemingly iOS is getting its own versions.
However while the Mac versions are used to edit PDF's, images and text files, the iOS versions are apparently optimized to simply let you view any such documents that you have stored in iCloud.
It's questionable how real this screenshot even is, 9to5Mac claims to have confirmed its veracity with several sources, yet it would be easy to fake, especially as the Text Edit and Preview icons are identical to their Mac counterparts.

iWatch connection?

There are still a multitude of rumors doing the rounds regarding the Apple iWatch, and with iOS 8 we could see functionality for a smartwatch built into the ecosystem.
A screenshot appeared on a Chinese social network allegedly showing the iOS 8 interface and a new app called "Watch Utility."
iOS 8 - LEAK
Will iOS 8 support an iWatch? (credit: @zmeric)
While we're not convinced of the screenshot's authenticity, it certainly does provide food for thought as the wearable market continues to develop and companies such as Samsung and Sony look to include such devices in their mobile operating systems.
The Watch Utility app has also appeared in a series of leaked images from Phone Arena, claiming to show iOS 8 running on an iPhone 5S.
As well as the Watch Utility app, the leak also shows Healthbook, iTunes Radio and other mooted applications such as Preview, TextEdit and Tips.

App updates

There are whispers of various minor updates to a number of apps. According to an unnamed source the Notification Center is getting streamlined for iOS 8. The update completely removes the "Missed" tab, so everything can be found on either "Today" or "All".
The Messages app is apparently having a new option added, to allow you to automatically delete threads after a certain period of time and Voice Memos may be getting a new button arrangement.
Apple is also supposedly removing the requirement for a Lightning cord when using CarPlay, allowing it to work wirelessly instead.
Apps may also be able to better communicate thanks to a new developer API which is rumored to be in testing. Known as an "XPC" service, the API would allow apps to share data, which among other things would hopefully make it easy to keep files synced up across different apps.

Split-screen apps

One iPad specific iOS 8 update that we've now got wind of is the ability to have two apps running side by side, split-screen on Apple's tablet. The screen is certainly big enough so it's a feature that makes sense, especially as Microsoft's Surface already has that ability.
Like so many other iOS 8 rumors this one comes from sources speaking to 9to5Mac and they go one further by claiming that the apps may be able to interact with one another. So for example you might be able to drag an image from one app to another, which would certainly make it more viable as a productivity focussed device.
Apparently the split-screen feature will only work in landscape mode and it's not clear whether it will be available on the iPad mini range or just the full sized models.

Goodbye Game Center

While there are a lot of new things rumored for iOS 8 we might also be losing some things. Apple's Game Center app is rumoured to be for the chopping block according to 9to5Mac, with the functionality being moved directly into games themselves.