WeChat, developed by Tencent, became one of the world's largest standalone mobile apps with over 1.2 billion monthly active users. Its success in gaining users can be attributed to several key factors:

1. Early Market Entry: WeChat was launched in January 2011, at a time when the mobile messaging landscape was still evolving. It capitalized on the growing popularity of smartphones in China and quickly gained traction by offering a comprehensive set of features beyond just messaging, such as social networking, mobile payments, gaming, and more.

2. Seamless User Experience: WeChat focused on providing a seamless and all-in-one user experience. It integrated various functionalities into a single app, eliminating the need for users to switch between different applications for different purposes. Users could chat with friends, share moments, make payments, order food, book taxis, play games, and more, all within the WeChat app.

3. Viral Growth through Word-of-Mouth: WeChat's user growth was largely driven by word-of-mouth recommendations. In the early days, users invited their friends and family to join the platform, which created a network effect. WeChat also incentivized users to invite others through referral programs, offering rewards and discounts for successful referrals.

4. Strong Social Networking Features: WeChat introduced innovative social networking features that encouraged user engagement and viral growth. For example, it introduced "Moments," a feature similar to Facebook's news feed, where users could share updates, photos, and videos with their contacts. This created a sense of community and encouraged users to spend more time on the platform.

5. Integration with Chinese Digital Ecosystem: WeChat integrated with various other services and platforms within the Chinese digital ecosystem. It partnered with e-commerce platforms like JD.com and Dianping, allowing users to make purchases, order food, and book services directly through the app. WeChat Pay, the app's mobile payment service, became widely accepted, further driving user adoption.

6. Marketing and Advertising Efforts: WeChat invested heavily in marketing and advertising to promote its platform. It collaborated with celebrities, influencers, and brands to create engaging campaigns and attract users. For example, it launched campaigns like "WeChat Shake" where users could shake their phones to find and connect with other users nearby, creating a buzz and attracting new users.

References:

1. WeChat - Wikipedia: https://en.wikipedia.org/wiki/WeChat
2. How WeChat became the primary news source in China: https://www.bbc.com/news/world-asia-china-51217455
3. WeChat's world: https://www.technologyreview.com/2013/04/18/174931/wechats-world/
4. How WeChat became China's app for everything: https://www.wired.co.uk/article/wechat-china-app-everything