That's currently not implemented, but definitely something we would like include. What I'd really like to see is a client for a bitcoin exchange. See our contribution request page for more details: https://github.com/quantopian/zipline/wiki/Contribution-Requ...

Finally, live trading is something which we are working on to enable on Quantopian (which uses zipline for backtesting your algorithms). The syntax is very similar so you could just convert your zipline strategy to Quantopian (which is free to use).

We are building just that at https://www.quantopian.com. It runs on zipline, and we're hooking it up to brokers.

For those with an account, E*TRADE offers a REST based API @ https://developer.etrade.com . Onboarding is manual but once you get your key you can execute trades for your account via the API. Equities / ETFs only right now, they were working on support for other asset types but not sure when they are going to launch it.

Full disclosure - I used to run their developer platform.

How do commissions work? per trade? Does the api provide any data, or just execution?

Commissions are the same as your E*TRADE account; list price is $9.99 for equities although if you are doing higher volumes you can negotiate discounts ($7.99 if you do 150 trades / quarter, and call them up if you are doing a lot of trades for lower pricing).

Data: https://developer.etrade.com/ctnt/dev-portal/getDetail?conte...

There's also a call for data on option chains.

If you're looking to do API trading as a retail customer, Interactive Brokers is the best I've found. 1/2 cent per share per trade with a $1 minimum commission per trade.

A downside is that they are between you and the exchanges at least when you use their SMART routing, so I get the impression your fills will be optimized for their benefit (via their Timber Hill subsidiary), not yours. Years ago, you could get filled substantially better than your limit order especially at the open for example, but no more.