EsperTech is the company behind Esper (Java based) and NEsper (.Net based). Development of Esper, which is open source – under a GPL license – was started in 2004, and EsperTech was founded in 2006. The company is based in New Jersey and does not have any other offices. The company is completely self-funded and has no sales force. Nevertheless, it has users world-wide (mostly in the banking, IoT, telecommunications and security) as well as OEMs that have embedded Esper into their own offerings.
Because of its open-source presence and large number of OEM/ISV partnerships EsperTech believes that Esper is probably the most widely used platform of its type world-wide. This is not an unreasonable claim.