Quantum computing is the current topic of interest from interdisciplinary researches. This paradigm has exposed more opportunities for researchers to harvest high-end computing capabilities to solve computationally intractable problems. Driven by great motivation toward the emergence of quantum computing, this paper is designed to serve as a guidance for readers (regardless of the research background) to indulge contemporary landscape of established (practically usable) quantum computers. This paper presents structured assessment on the classes of quantum computers, quantum technologies tied to each class of quantum computers, and service providers (companies) for each quantum technology, with no claim to completeness.