A few potential competitors from a list I had built earlier this year (unrelated project):

http://www.getpose.com/

http://www.erply.com/

http://www.vendhq.com/

http://www.cashierlive.com/

http://www.merchantos.com/

http://www.camcommerce.com/

http://www.posterita.com/

http://shopkeep.com/