begin

[syntax] begin expr expr2 ...

R5RS, R6RS

Some implementations allow begin with no exprs: Chicken, STk, Gauche

[module clause] begin expr ...

Chicken: this form can be used in the module clause in define-module. See Chicken:ModuleSystem?.

[configuration language] begin expr ...

Scheme48: used in configuration language. See Scheme48:ModuleSystem.