As successful Trading application you need following three things.
1 Ultra low latency application in highly volatile market. I would write multi Threaded code so you can match up with fast moving market
2 Highly Quality code. I generally follow test driven approach so you can get high quality code because a single bug can cost you a lot.
3 Low maintenance cost. To achieve high profit your strategy should be accurate and recurring cost should be low. I use Open source (java/python) and nosql database which provide highly scalable and low recurring cost.
I have worked more then 50 trading application in my last 8 year. I worked with Equity, Forex, Future/Option,Binary Option, Bonds(FixedIncome) Trading.
I worked in each part of Trading life cycle (Market data,Order managment system,STP,Clearing house,Risk management,BackTetsing/Pre Trade Compliance/Post Trade Compliance). I use FIX/FAST ,costume api of borker(Inertactive broker,FXCM etc),traina.
I am including some of my projects for your reference. some of project are from freelancer or upworks so i can show you those on my profile(I can't give link because that would not get opened from your login)
High Frequency Trading with FIX(olfa/hotspot):-
This project was build for UK client. This is connecting with Olfa and Hotspot. This is co-located solution and use FIX for market/oms connectivity. This is optimized up to microsecond level.