1. IB interactive brokers realtime api TWS-APi.
You can start demo acct to make realtime work for you.
2. Iex Exchange Api..this changed on june 1st..but it is professional level api
3. Alpaca.markets api..also need to get demo acct and token
4. Esignal Api
Now pleas allow us a realtime grid to monitor our in trade portfolios so we can get mechanical exits and alerts
Also please consider a api interface to the data and grids so we can apply our own logic to the program for alerts, buys, sells, and mechanical systems.
Consider embedding a MONO csharp compiler and a Fortran Compiler..so we can use some codes we own in the indictors systems, and alerts.
Please add some sms texting alerts ...thanks.ric