Matryoshka is a communications mechanism that uses multiple nodes with direct connections exchanging a continuous stream of fixed length packets.
When one user sends a message to another, such as an email, the originating computer decides a random path, arranges the path by establishing each connection through the previous, and then finally sends the message.
For each layer of communications the message is uniquely encrypted.
This allows end to end communications with no intermediary or external party having the raw data or metadata.
There is no evidence communications ever takes place.