Exactly as JimBoone has said. What I will say about ReservationKey is that there are innkeepers in the UK who were looking to change what they had and I told them about RezKey as we call it for brevity. I know of several who use it now. Most take deposits (I do not), many have the credit card number entered - so the deposit can be taken & RezKey has that to have to do the proof with) I prefer to call them to get the # and it gives me a chance to find out if it is a special visit, getaway, or pass-through. It has reports, yield management, add-ons, you can set it to # of nights required for certain dates, stayovers or departing reports for housekeepers, all sorts of reports and abilities - most of which I do not use with 3 rooms and no staff. But it has what is needed by small to quite large facilities. He was just getting started when I signed on. As innkeepers discovered features they wanted and asked for, those features were added.
What got me hooked was the fee is tiered to number of rooms so I am not paying the same gee as JimBoone with his 8 rooms (the ROI would be great for him but not for me. The support is great and there is also a user Forum to ask questions - like here - how do I do this, this is what is happening so how do I fix. It is the one I know and it DOES interface with the OTAs if you wish to go that route. Look at them, features, costs, Support, auto-responses to guests (YOU write them so it is what YOU want to say and you can personalize the Thank you for your stay before the basic one goes out or just let it go as is).