According to the Financial Times, there were 40,000 downloads of the app in Iraq last week, despite the fact the country has no iTunes store.
User numbers in Iran spiked when the socially conservative government banned Whatsapp, a popular instant messaging application. The app is also available on Android.
What is FireChat?
FireChat connects people using bluetooth rather than mobile networks or internet connections, meaning users can send messages in places like the underground where signal is limited. Increasingly, however, the app is gaining popularity in countries where governments control access to the internet.
People with the app communicate in chat rooms set up around different themes. The most popular in the US, where the app is most used, is centred around Game of Thrones.
The app is run by a team of 10 from its base on an island in San Francisco Bay.
How does it work?
FireChat is designed to work using wireless mesh networking, where a string of devices connect to each other using nodes, which do not require the internet to function. The application uses bluetooth and has a range of 70 metres, but users can use other mobiles as stepping stones, creating a web of contacts spanning much larger distances.
This makes the app particularly useful in countries where the internet is restricted such as Iraq and Iran, which sit second and third respectively on the list of countries where Firechat has received most usage.
FireChat's popularity may also be based on the fact that it is much harder for governments to monitor communication on a mesh network, an issue important to many in the wake of the Edward Snowden revelations.