Dendron has many moving parts but at the core, it consists of a traditional client/server model.
Currently, the clients are:
The server is a local express.js server, more details on that here.
Dendron also has many utility packages and libraries that are used in both client and servers of Dendron. You can find an index of all Dendron packages here.
The plugin architecture is described in Dendron Plugin Architecture
The server architecutre is described in Dendron Engine Architecture