Mainly a VDOM with some convenience features.
Ranked in these QuestionsQuestion Ranking
Use it however you want in a framework of your own custom design. When things change in the industry, swap things out instead of being locked in by someone else's design.
Pro Fast VirtualDOM
Inferno has one of the fastest VirtualDOMs out there.
Pro Pretty light-weight
Inferno weighs in at 9kb gzipped, which is light-weight.
Pro React compatability
Using the Inferno compatibility package ("inferno-compat"), Inferno can support the vast majority of React codebases.
Con Not very popular
Which can hinder one's opinion of its future, but the future of all "frameworks" is to break things into smaller pieces, so inferno very well might get used by the big names in the future.