Here is a list of all modules:
[detail level 12345]
 BoardsBoard specific definitions and implementations
 CPUCPU specific implementations
 Compile time configurationsList of compile-time configurations
 DS3234 Extremely Accurate SPI RTCDriver for Maxim DS3234 Extremely Accurate SPI Bus RTC with Integrated Crystal and SRAM
 DriversDrivers for external devices as radios, sensors, memory etc
 KernelThe RIOT micro-kernel containing the core functionality
 NetworkingNetworking libraries
 PackagesExternal libraries and applications
 SystemSystem library contains tools and utilities that make RIOT an actual operating system
 UtilitiesUtilities and helper functionality