Thanks for that article. Some thoughts, from having worked in the field for the past couple of years: I've noticed that many of the tier 1 IBs (sell-side) have inhouse-developed platforms for algo trading (in C++ or Java), so I guess the vendors are competing for the smaller brokers' attention, and of course, the huge buy-side market. Whoever wins, Event Stream Processing (ESP) is a great concept and would really benefit the design of event-driven systems. Right now, the tier 1 IBs are stuck with older generation designs (typical OO) in which they have invested a lot of time and effort, and ESP will make it into their heads and code base only on the next iteration. IT/software design is important for scalability but lest the IT focus detract too much : what keeps tier 1 ahead of any 3rd party system is the quality of quants and their insight into the Efficient Trading Frontier principles & transaction cost analysis.