The MessagePack format is a binary serialization format for storing data much like JSON except it is smaller and faster. There are libraries for over 50 programming languages out there and there are two different MsgPack libraries which should work in Delphi XE8 Firemonkey. These libraries should work cross platform on Android, IOS, OSX, and Windows. The first library is called QMsgPack by chinawsb and it is also found in the QDAC library. The second library is called TSimpleMsgPack and it is by Github user ymofen. Apparently the MessagePack format takes up less memory and less disk space to store data with. Additionally, it looks like it is faster to work with the MessagePack format than JSON. Pinterest and redis are two companies that are listed as using the MessagePack format. All of the different MessagePack format libraries should allow you to create/process MessagePack files in Delphi and then create/process those same files on the server of your choice whether it is PHP, Python, ASP.NET, etc. I would be interested to see some benchmarks comparing the speed of the Object Pascal MessagePack libraries against some of the Object Pascal JSON solutions. The source for the MessagePack libraries is free and they should also work with Appmethod.
Download the QMsgPack library for Delphi XE8 Firemonkey from Github. A newer version may be available from the QDAC site.