Brokers like Interactive Brokers, Tradestation, MB Trading, TD Ameritrade and eTrade to name a few, all have there own order routing technologies. I guess you could call it proprietary technology though they often will expose their technology via an api.
Brokers like Mirus, as far as I know, down have there own order routing technologies, so they offer a 3rd party solution like zen-fire or Pats or Trading Technologies.
So breaking it down to the basics, to trade you need:
1) Data - Realtime and/or Historical and/or end-of-day.
2) Order routing - To various exchanges depending on what you want to trade. Some go to all exchanges and some go to just a few.
3) Clearing firm - A Broker may or may not be a clearing firm those that aren't have some sort of relation with one though. Some clearing firms will clear at all exchanges and some will clear at just a few.
There are various ways to achieve this. This should all be factored into selecting a broker(s), a data provider and an order routing technology.
With the brokers I mentioned in the first paragraph, they are an all-in-one solution. Brokers like Mirus are not. That is not necessarily good or bad. The marketplace has room for both.
cT