First is the basic TD Ameritrade Mobile app, which gives you much of the power you have on your desktop stock trading app in a mobile experience for iOS, Android, and Windows phones. Missing chart analyzing function. The best overall stock trading app experience comes from TD Ameritrade , one of the largest brokerage firms in the country. Stocktwits is a great app for sharing and watching others trading ideas. Buying and selling stock investments used to require a phone call to a stockbroker who would charge you an arm and a leg to execute your stock trade. Trading apps can be used for trading, learning, charting, finding trading ideas, and also for market data and news.