Robinhood - Free stock trading service.
Alpaca - Open links from Slack via desktop apps: Notion, Spotify, Zoom, Miro, Telegram, Airtable, Figma and VK.
Trigger Finance - IFTTT for the stock market
Bullish.email - The Stock Market in your inbox every morning
SysGears Grain Framework - The simplest way to start investing.
StockData.org - Free real-time, intraday and historical stock market, crypto and forex JSON APIs.