Built and maintained a client and market side booking service, off order book trade reporting engine and trade manager/repository
Like most banks, this one suffered from the not invented here syndrome. They had decided to pretty much reimplement the core libraries to optimize for Zero Garbage Collection, low latency and high throughput. Unfortunately they were not optimized for large development teams and maintainability.
I helped the team debug issues and introduce new functionality using a tech stack that consisted of Java, Groovy, Spring, FIX, JUnit, MSSQL and JRebel.