There used to be quite a few different mainframes on the market. HP/Tandem had their Non-stop systems which was perhaps the most distinct competitor - but there

There used to be quite a few different mainframes on the market. HP/Tandem had their Non-stop systems which was perhaps the most distinct competitor - but there were quite a few companies competing in the space. However, IBM has dominated this market for as long as I can remember and today I believe they are the only ones making mainframe computers.