solana-msg is used at run time in 129 crates (of which 1 optionally). It is a direct run-time dependency in 11 crates. It's used only as a dev dependency in 4 crates.

Depender (with downloads and own rev deps) solana-msg version
1.1M 546 solana-program =2.1.0
196K 5 spl-tlv-account-resolution ^2.1.0
195K 5 spl-transfer-hook-interface ^2.1.0
181K 25 spl-pod ^2.1.0
180K 17 spl-type-length-value ^2.1.0
176K 33 spl-memo ^2.1.0
177K 21 spl-token-metadata-interface ^2.1.0
170K 16 spl-token-group-interface ^2.1.0
6.2K 5 solana-program-entrypoint =2.1.0
6.1K 15 solana-program-error =2.1.0
4.4K 1 spl-record ^2.1.0