This list is representative of what came to my mind...

Apple:

• Beats
• Siri

Amazon owns:

• Blink Home Automations
• Cloud9 DNS
• Double Helix Games
• Drugstore.com
• Gear.com
• IMDB
• Pets.com
• Ring the security camera/doorbell company
• Twitch
• Wondery the podcast thingie
• Woot
• Zappos

Facebook owns:

• Friendster
• Giphy
• Instagram
• Oculus
• WhatsApp

Google/Alphabet owns:

• Adscape
• Apigee (for our coder pedes)
• Dodgeball (Social Media)
• DoubleClick
• Dropcam (Home security)
• Fitbit (the wearable company)
• GrandCentral (VoIP)
• HTC (the cellphone maker)
• Kaggle (for our data science pedes)
• Looker (for our data science pedes)
• Meebo (Social Media)
• Nest (the home security company)
• Plink (Image Search)
• Quickoffice (Productivity Tools)
• reCAPTCHA
• SageTV
• Slide.com (Online Gaming)
• Sparrow (Mobile App)
• Tenor (Image search)
• Waze (the GPS app)
• YouTube
• Zagat (the restaurant guide)

This list is representative of what came to my mind...

Amazon owns:

• Blink Home Automations
• Cloud9 DNS
• Double Helix Games
• Drugstore.com
• Gear.com
• IMDB
• Pets.com
• Ring the security camera/doorbell company
• Twitch
• Wondery the podcast thingie
• Woot
• Zappos

Facebook owns:

• Friendster
• Giphy
• Instagram
• Oculus
• WhatsApp

Google/Alphabet owns:

• Adscape
• Apigee (for our coder pedes)
• Dodgeball (Social Media)
• DoubleClick
• Dropcam (Home security)
• Fitbit (the wearable company)
• GrandCentral (VoIP)
• HTC (the cellphone maker)
• Kaggle (for our data science pedes)
• Looker (for our data science pedes)
• Meebo (Social Media)
• Nest (the home security company)
• Plink (Image Search)
• Quickoffice (Productivity Tools)
• reCAPTCHA
• SageTV
• Slide.com (Online Gaming)
• Sparrow (Mobile App)
• Tenor (Image search)
• Waze (the GPS app)
• YouTube
• Zagat (the restaurant guide)