NLT is free, open-source C# lexer and GLR parser suite -- which translates to ability to parse ambiguous grammars. Grammar can be defined directly in code or (preferably) in separate file (lex/yacc-like) for included generator.
If you understand/guess the meaning of grammar in C#:
// scanning
lexer.AddStringRule(")", match => SymbolEnum.RPAREN);
// parsing
prod_builder.AddProduction(SymbolEnum.exp,
SymbolEnum.LPAREN, SymbolEnum.exp...