A key element of a contract is that each party is exchanging something of value in consideration for the value it will receive. That consideration may be intangible or a future benefit, but without consideration, in many jurisdictions a lack of consideration means that no legal contract exists.
In common law an alternative to a contract is a ‘deed’ which is a binding promise. Some jurisdictions require special procedures for a deed to be enforceable, for example that it be notarised. It is not uncommon for certain types of agreement to be styled and described as both a contract and a deed.