It's a bytecode loader for gmod servers

local bytecode = string.dump(function() print "my secrit code" end)
-- 10 minutes later
require("gmbc")
gmbc_load_bytecode(bytecode)()

1. Rust (https://www.rust-lang.org/tools/install)
   1. Note: Rust may depend on a separate compiler on your platform, such as Visual Studio, GCC, etc:
      1. Windows: Install Visual Studio 2019
      2. Linux: Install gcc-multilib
2. (Optional) Additional Rust toolchains for compiling 32-bit binaries:

rustup target add i686-pc-windows-msvc # Windows
rustup target add i686-unknown-linux-gnu # Linux

git clone https://github.com/willox/gmbc
cd gmbc
cargo build --release --target=i686-pc-windows-msvc # 32-bit
cargo build --release --target=x86_64-pc-windows-msvc # 64-bit

You can then find gmbc.dll in ./target/<target>/release. Rename it to gmsv_gmbc_win32.dll or gmsv_gmbc_win64.dll and you are done.

git clone https://github.com/willox/gmbc
cd gmbc
cargo build --release --target=i686-unknown-linux-gnu # 32-bit
cargo build --release --target=x86_64-unknown-linux-gnu # 64-bit

You can then find gmbc.so in ./target/<target>/release. Rename it to gmsv_gmbc_linux.dll or gmsv_gmbc_linux64.dll and you are done.