What I get paid or have been paid to do:
Trading software and protocols (QuickFIX, Onix, etc).
Price feed development.
Trader simulation tools.
Back office, end of day reporting, NFA compliance.
Performance testing, optimization, and analysis.
Large scale data management, analysis, and visualization.
Worked with most major banks, some electronic exchanges, many data providors, and a few counter-parties:
MISO, PJM, NYISO, NEISO, CAISO, AESO, ERCOT, BOE, CME, CBOE, Eurex, ICE, Morgan Stanley, J.P. Morgan, RBS, EBS, Credit Suisse, Nomura, Barclays, Deutsche Bank, Citibank, UBS, Goldman Sachs, Bear Stearns (defunct), Triaina, Bloomberg
Experience in FX, energies, futures.