The Bitcoin Open Ledger Operating System (BOLOS) is Ledger platform allowing developers to create pluggable applications on their Hardware Wallets.

BOLOS offers a minimal common set of features for all platforms :

Access to the main Hierarchical Deterministic wallet of the user in bolos_wallet.h
Basic cryptographic APIs (symmetric and asymmetric ciphers, hashes) in bolos_crypto.h
Methods to exchange data between sessions and bind data to applications in bolos_wrapping.h
Methods to verify the authenticity of the hardware and the code in bolos_endorsement.h and bolos_attestation.h

The implementation of BOLOS for a Trusted Execution Environment also features dedicated APIs :

Specific interface calls for a virtualized platform in bolos_core.h and bolos_utils.h
Simple User Interface (when a Trusted User Interface is available) in bolos_ui.h
New generation cryptographic primitives with NaCl / libsodium in bolos_sodium.h

On the TEE, BOLOS isolation is done by running a Moxie Virtual CPU - for more details about setting up the environment, refer to https://github.com/LedgerHQ/bolos-tee