I would propose the term hybrid:
hybrid - a thing made by combining two different elements; a mixture
By analogy from agriculture, it could casually be called a cross, as in a cross between A and B where A and B (… Z) are its components.
A mattock is a cross between a pick and an adze.
In certain fields, notably music and web-based software applications, the term mashup has currency. A song mashup combines two or more pre-recorded songs into a new composition. A web mashup is typically a presentation combining data from multiple sources, for example displaying the sources of Tweets on a Google Map. But only the most vacuous analyst or marketer would call a spork or a mattock a mashup.
A more derisive term would be bastard, which connotes some imperfection in or prejudice against either the lineage or the combination, and is mildly offensive in some quarters. MacOS is the bastard of the Mach kernel and BSD.