The best apps for expats in China

The APPS that I use are;

WeChat (Everyone uses it. It's difficult to get around in China without it.)
QQ (I don't use it that much any more.)
Skype (It is the preferred method to talking outside of China.)
163 (Forget about using a Western email address. Use 163 for free.)

Other APPS include

E Le Ma (To order food and have delivered to you. You just click on the photo.)
OFO (One of many ride-share bicycles)
Tao Bao (Order things from the Internet.  Sort of a Chinese Ebay.)

There are some very good translation APPS. There are some that you can speak in to with English and it translates into Chinese characters.  Very useful in a KTV environment.  However, the APP loads all sorts of games, advertisements and nonsense advertisements on to your phone.  So I deleted those that I had tried out.

As VANNROX said, WeChat is probably the most useful app in China - not just for communication, but also for payments, news, local information and locating your friend when you realise you have turned up at the wrong Starbucks on West Nanjing Road. I've even found that when doing business with Chinese, WeChat is preferred over email. In my experience, you're almost always guaranteed to get a response by WeChat and the same cannot be said for email here.

My other most-used apps include:

A VPN - I won't name the one I use, but if you want access to Google, Facebook, Pinterest, Bloomberg, Twitter and various other blocked sites, you're going to need a VPN.
Baidu Maps - essential 'sat nav' for driving around Shanghai. Actually, pretty good if you're getting around on foot too.
Xe.com - currency conversion tool.
Pleco - a really good (free) Chinese-English dictionary. It also comes with built-in flashcard tests, so you can learn characters on your Metro journey or waiting for your turn in the bank.
China Air Quality - it's usually quite obvious when looking out of the window as to the state of the air, but it's good to get the official readings to back up your senses,, especially if you have young kids and you're planning to spend the day outside. I think the air quality in Shanghai has been improving over the last few years, but there are still bad days, particularly at this time of year.
Metro Man - a great app to help you navigate the already-sprawling and ever-expanding Shanghai Metro. Most other cities in China with metro systems seem to have their own versions too.
iQiYi and PPTV - you can stream a lot of great British/American tv series and films. And, of course, Chinese, if you're into them.
YouKu - Great Chinese alternative to YouTube if you don't have a VPN.
Spotify - coz you gotta have some tunes on your phone!

Most most commonly used apps - The first 2 at least is a must-have. The rest, will depend on your level of mandarin and how savvy you are.

Wechat - Messaging and Payment system
Alipay - For the payment System
Didi - The Chinese version of Uber (linked to your alipay/wechat pay)
Shenzhou Zhuan Che - Premium version of Uber like Uber Black (super safe, and super reliable, but comes at a premium.(linked to your alipay/wechat pay)
Meituan - The super app - It's like a suped up version of groupon, discount coupons, and every other discount coupon app you can think of (but a lot better), Restaurant review.(linked to your alipay/wechat pay)

TheChariman'sBao75' value='35806'>[link under review], Telegram
AQI: [url=/][url=/]Airpocalypse[/url][/url]
Chinese Language: Hanping Dictionary, TutorMandarin, TheChariman'sBao, HelloChinese, [link moderated]
Food: HaiDiLao App, Sherpas,

EXPRESS VPN OR ASTRILL

WE CHAT

DIDI - TAXI APP

QQ MAIL

CTRIP - TRAVEL APP NOW CALLED TRIP.COM

STARBUCKS APP

YAHOO MAIL

VIBER

Of course, the most important app is WeChat. It's hard to explain in the West what all the benefits of WeChat are.
Besides WeChat I use Baidu Translate as my Main translation app.
To learn Mandarine, I use: (Udemy) Chinese Made Easy, DuoLing, Flashcardsrds. I have more but I hardly use the otherones.
Currency (XE), to calculate the currencies
Metroman
Maps
camera
photo's
Agoda
Trip
Ofo
Strong VPN

I guess this is about it!

Here's one nobody's menthoned yet: select-1.launchrock.com/ ... It's like the ultimate way to keep in touch with friends you have in a different city, which happenes alot in China. 

Its all about Wechat for me. I pay my bills, order food, pay street vendors and more on it.
On top of that i use:
thepiratebay.org for all films and series, even if they have just come out
Mobike for bike share (Amap seems to work for both Offo and Mobike though)
Ctrip: train travel
Booking.com: hotels
Shanghai Metro: tube travel
Bon Apps: food and taxi
maps me: travel, taxis, hotels
me fit band: health
BBC iplayer: keeping in contact with England
Alipay: back up for Wechat pay
China Air Quality: for pollution

Hope this helps