Brokers generally have their own in-house platform which is web-based, however there are third party platforms which are open source and provide freedom to build your own custom indicators.
Meta Trader 4 (MT4)
Meta trader is an open source platform which many FX brokers use. It’s open platform means that developers are able to create indicators and signals that are very useful for your trading. You may find that brokers have MT4 along with their own in-house solution. MT4 is primarily based on the Windows operating system, however there have been attempts to make it compatible with Mac OSX. You may wish to look at Forex VPS if you can’t get it running natively on your own machine.
Make sure you download the MT4 version from your broker. They should provide easy instruction setup with account details
You can also find other great tips, tools and resources recommended by Joel.Forex Tools & Resources