If all else fails, sites like lumiafirmware.com appear to have archived all the device images from Microsoft's servers. Actually flashing them on is VERY non-trivial, so I'll save a tutorial for when the official utilities break! Update: Lumiafirmware is down, so try http://cellomania.com/ffu/ 

Edge remains a competent browser for most plain sites. But its development stopped as of Windows 10 branch 1703 almost four years ago, effectively, since the 1709 branch's Edge wasn't fully rounded out (in terms of service worker and other background operation). Which makes it something of a dead end if you're looking for more. Third party browsers all ultimately have the same underlying restrictions for PWAs and some other HTML5-reliant sites. Roughly half the PWAs out there work, roughly half don't - see the Flow column on AAWP for recommendations of the former!

Just as when Symbian's Web browser was deemed old hat in 2013-2015 because web sites and technologies had 'moved on', the same is largely true now for Edge (in v1709). Pages have grown since 2015, web technologies have evolved, and precisely zero web developers are testing against such an old (2016 era) browser. C'est la vie.

I'm just making the point that Edge was actually pretty great when it launched in Windows 10 Mobile at the time. It's the world that has changed...!

^* This syndrome isn't unknown. No one at Microsoft has been specifically tasked with shutting the server off, so things will probably now just keep working until an infrastructure change for some other system physically impacts the backup servers!

Until 'March 2021', which was a year ago! In theory, if you hard reset a Windows 10 Mobile phone now then you'd have to rebuild it manually, installing from the Store, etc. Which will still hopefully function. I'll post a tutorial and check list as and when this definitely stops working. There's every chance that Microsoft will forget about turning this system off too!

Mind you, there's a school of thought which says that it's always best to build an app set-up from scratch anyway, in order not to put back stuff you don't actually need. PIM stuff and photos will come via the cloud and OneDrive etc. It's an option, anyway, going forwards, so do make sure that you have non-synced data and documents on your phone copied onto other devices and media, as needed.

Notably, the trickle of new UWP applications in the Store has now pretty much dried up, and only a handful of popular titles are still receiving updates. The developer world has (understandably) moved on. But it's still important to have the Store fully available, in case you have to reset and restore a Lumia, since latest binaries come from here as part of the restore process.

It's worth noting that the OneDrive client on iOS and Android is excellent - if you do switch at some point then you essentially carry on with the same interface, auto-backup, and photo stream in the cloud (subject to your storage plan, e.g. 1TB with Office Microsoft 365)

This being a cloud-centric OCR solution, it's utterly dependent on Microsoft allowing server access. It was announced that access to the OneDrive servers would stop at the end of 2020, and this has now happened, for Office Lens on both Mobile and Desktop. The idea is that the iOS and Android versions of Office include the same functionality and will be more convenient for most people. Go figure.

No cessation date announced, likely 2022 or beyond. Outlook app development is all on newer Windows 10 branches though, so the current one on Windows 10 Mobile is only receiving small bug fixes and none of the sexier stuff you'll read about in the news.

Of worrying note is that auto-configuration of new major email/PIM accounts doesn't now work. I've tested setting up a Google account to work with Outlook on a reset phone and changes at Google's end mean that the relevant password and set up screens don't get handled properly. Similarly for Yahoo, and possibly others.

Note that existing phones with previously setup accounts will carry on working fine - the caveat above is for adding accounts to a Windows 10 Mobile phone. Plus native Microsoft email/PIM accounts are fine.

No official cessation date announced. 'Automatically update maps' seems to still work (i.e. doesn't throw up a server error) as of the start of 2022, but actual updates have now stopped - I haven't had anything offered since January 2021. Time will tell, etc! Ironically, HERE Maps/Drive and offline maps updates still work perfectly for 'ye olde' Windows Phone 8.1 because they're driven by HERE, not by Microsoft.

Official client is a PWA, but works well (if already installed), apart from lack of push notifications to the Edge engine used (the usual lack of 'service workers' in the browser). Here's the latest changelog. API limitations at Twitter's end mean that there's now no fully working third party alternative (at least, one that also has access to DMs). 

However, of note is that this has now disappeared from the Store, so there's no way to install it again on a reset device, which is a huge shame. In that case, you'd have to use the PWA (twitter.com) in the Edge mobile browser. Which does the same thing, but you have to live with the browser URL bar etc.

The Twitter code is starting to lag a bit on the low power older Lumias, mind you - and it's only going to get worse as Twitter's coders add more and more stuff!

Official (Osmeta-based, derived from iOS codebase) client has now been withdrawn, being part of the Facebook 'empire'. There's an official Instagram PWA, but it's officially available patchily under Windows 10 Mobile, available as an upgrade through the Store only if you have the original installed. Very odd - it's not there otherwise. But don't despair, as the PWA has been recently upgraded and is available to anyone as a simple URL/favourite in the Edge browser.

There are also several third party alternatives, the clear favourite of which is the quirky, often unstable, but always improving Winsta UWP (which now features notifications).

The official WP8.1 application still technically runs, but has now lost search functions and is clearly on the way out. Various third party applications were targetted by Spotify's lawyers and have now been withdrawn from the Store, sadly. Spotimo UWP was your best bet, and was reworked as 'Strix Music', and this is available for side-loading. Not ideal, but its 'LTS' (Long Term Support) version (v1.4.9 as I write this) does 'kind of' work and it's not too onerous to get it installed. Expect glitches galore, so be patient with it - it's all we've got!

This has now stopped working completely with Windows 10 Mobile...

One of the more famous spats between Google and Microsoft, this hasn't had an official application for years, though of course it works fine in the Edge browser. I'd recommend myTube! or Awesome Tube though, both UWP applications with slick interfaces and all kept up to date. Hopefully. YouTube does keep changing things though, so have both UWP apps installed and go for the one updated most recently.

There was a new client, LikeTube, but that seems to have been pulled. I'll investigate.