Here is a list of all modules:
[detail level 12]
 Data Channel Compression moduleThis module offers compression of data channel packets
 Control Channel Processor moduleThis module controls the setup and maintenance of VPN tunnels and the associated security parameters
 Control Channel TLS moduleThis module provides secure encapsulation of control channel messages exchanged between OpenVPN peers
 Control channel encryption (--tls-crypt)
 Data Channel Control moduleThis module controls the processing of packets as they pass through the data channel
 Main Event Loop moduleThis main event loop module drives the packet processing of OpenVPN
 Data Channel Fragmentation moduleThe Data Channel Fragmentation module offers fragmentation of data channel packets
 Reliability Layer moduleThe Reliability Layer is part of OpenVPN's control channel
 Data Channel Crypto moduleThe Data Channel Crypto Module performs cryptographic operations on data channel packets
 External Multiplexer moduleThe External Multiplexer is the link between the external network interface and the other OpenVPN modules
 Internal Multiplexer moduleThe Internal Multiplexer is the link between the virtual tun/tap network interface and the Data Channel Control module