There are many sources and conflicting reports on what is available for people. We have simplified things for you:

On exchange:

An on exchange health plan is implemented within a government-run insurance marketplace. If one qualifies for a subsidy, it may be reason to utilize an exchange for enrollment. Premium subsidies and cost reductions for low-income applicants are only attainable on exchange, even if the same policy is available off exchange. Exchange participation by insurers fluctuates by state, so one should verify that quality doctors, hospitals, and other practices in your area are comprised within the health plan's provider network. An exchange may have different regulations from an off-exchange plan, even if it is through the same insurance company.

Off exchange:

An off exchange plan meets the requirements of Obamacare, but is not available for purchase on the government-run marketplace. It is feasable that the same plan from the same insurance carrier may have differences, between being an on or off exchange version. Not all plans sold off exchange are available on exchange. If the same plan is offered on, and off exchange, the premium should be identical for the applicant. However, applicants with low income may qualify for premium subsidies that are only available on exchange. Off exchange may be purchased from a broker or agent, directly from an insurance company, or from an exchange not government-run.

Short-term:

Short-term insurance plans provide coverage for a limited time, an optimal solution for periods of unemployment. Short-term plans are generally 6 month, or 12 month terms. Any person that may likely need a plan longer than this may want to look into a basic, long-term health plan. The application process is typically simpler than standard insurance plans. These plans are constructed to cover unanticipated accidents and illnesses, rather than providing extensive coverage, and usually do not include preventive care, eye care, and dental. Short-term health plans do not cover per-existing conditions, which is defined on a state-by-state basis.

Indemnity:

Indemnity health plans grant you access to virtually any hospital or doctor you may choose. They are frequently called “fee-for-service” plans, the insurance company will pay a fixed rate of the charges. This amount is called the UCR (usual, customary and reasonable) rate for the service. You will likely have to pay a deductible before the insurance company will begin covering your claims. Referrals are not needed under indemnity plans, and you are not required to choose a primary care physician. This kind of plan may be right for you if you are looking for the maximum level of freedom possible in choosing your doctors, you don't want to receive referrals, and if you wish to freely visit any physician of your choosing.