ThingSpeak - Open source data platform for the Internet of Things. ThingSpeak Features
Firebase - Firebase is a cloud service designed to power real-time, collaborative applications for mobile and web.
dweet.io - Ridiculously simple data sharing for the Internet of Things.
Supabase - An open source Firebase alternative
Xively - Xively offers an Internet of Things product relationship management solution for enterprises.
Etebase - Etebase makes it easy to build end-to-end encrypted applications by taking care of the encryption and its related challenges.