Peer to peer android and iOS with Wifi direct (multipeer connectivity?)
I am very interested in this subject as well and I came across these links
AllJoyn
AllJoyn® is a collaborative open-source software framework that makesit easy for developers to write applications that can discover nearbydevices, and communicate with each other directly regardless ofbrands, categories, transports, and OSes without the need of the cloudSource: https://github.com/alljoyn/alljoyn.github.com/wiki
OpenPeer SDK
Open Peer is an open P2P signalling protocolSource: http://openpeer.org/open-peer-sdk-for-ios/
Microsoft's Project Rome
"Project Rome" is a project code name for Microsoft's cross-deviceexperiences platform using the Microsoft Graph. Source: https://docs.microsoft.com/en-us/windows/uwp/launch-resume/communicate-with-a-remote-app-service
Mutipeer connectivity cannot connect iOS and Android devices. Firechat is using its own implementation.
More information here:
A couple of weeks after its iOS launch, FireChat made its debut on Android. Since Android doesn’t support Apple’s Multipeer Connectivity Framework, developer Open Garden had to build its own mesh networking technology to enable off-the-grid messaging across Android devices.However, FireChat messaging hasn’t been possible between iOS and Android. That is, until now.Open Garden has just updated FireChat to allow for off-the-grid messaging even between iOS and Android devices.While it declines to reveal the exact details of how it managed to make Apple’s multi-peer framework and its Android mesh network connect with each other, Open Garden has told TechCrunch that its cross-platform capability uses peer-to-peer Wi-Fi and Bluetooth personal area networking.
Something like text chat can be done over BLE, which is open on both platforms. Sending images would be slow, though, since it doesn't have the throughput of Bluetooth Classic.