Interactive Brokers (platform and broker)

www.interactivebrokers.com
Allows lots of connectivity for outside platforms, no built-in algo tools, all third party, has options
Software List
www.interactivebrokers.com/Universal/servlet/MarketPlace.MarketPlaceServlet
Charting
https://gdcdyn.interactivebrokers.com/Universal/servlet/AccountAccess.AuthenticateSSO?action=ACCT_MGMT_MAIN&loginType=1&clt=0
Chat
http://chatsrv1.interactivebrokers.com/fchat/chat/flashchat.php
Elite Traders might be a good user forum https://www.google.com/search?sourceid=chrome-psyapi2&ion=1&espv=2&ie=UTF-8&q=elite%20traders&oq=elite%20traders&aqs=chrome..69i57j0l5.3711j0j8