Are there low cost airlines to travel within the US?

I always thought that the concept of low-cost airline, or no-frill airlines originates from the US.

According to Wikipedia, the following low-cost airlines can be found in the US. [updated 22/May/2017]:

• JetBlue Airways - Domestic, Mexico, Caribbean, Central and South America
• Southwest Airlines - Domestic, Mexico, Caribbean, and Central America
• Sun Country Airlines - Domestic, Mexico, Caribbean, and Central America

"Ultra" low-cost (no-frills) airlines:

• Allegiant Air - Domestic Routes and International Charter
• Frontier Airlines - Domestic, Mexico, and Caribbean Routes
• Spirit Airlines - Domestic, Caribbean, Central and South America Routes

Another LCC, Virgin America, was acquired by full-service carrier Alaska Airlines in 2016 and is being integrated into the latter's network.

There are a few airlines which operate flights at lower fares. I don't know if it is the same "low-cost" concept as known in Europe. Some names that I remember are

• Southwest
• jetBlue
• Virgin America

I personally experienced Virgin America. Tickets have to be purchased online and it's $15 for each bag checked as hold baggage. As opposite to Ryanair, most of the aforementioned airlines operate on the same airports as regular airlines and use terminals with the same amenities. One exception is that, in the Los Angeles area, jetBlue lands in Long Beach (LGB) instead of the main Los Angeles airport (LAX).

Spirit Airlines and SouthWest are both "low cost", although SouthWest has become more expensive over the past few years or so.