IMHO for small projects where entities are generated in response to a manual action of a user (i.e. relatively rare - the chance 2 users on different machines

IMHO for small projects where entities are generated in response to a manual action of a user (i.e. relatively rare - the chance 2 users on different machines do it in exactly same moment is very low) or everything is done in one thread on one machine a nanosecond/microsecond timestamp makes a practical unique identifier.