ThingSpeak - Open source data platform for the Internet of Things. ThingSpeak Features
PlatformIO - Next-generation IDE for IoT
The IoT Guru - the IoT cloud backend company
B4R - Development tool for native Arduino programs.
IoTPlotter - IoTPlotter.com is a service which collects data from your IoT devices for long-term graph plotting and storage. It's completely free and made for the maker community.
openHAB - "empowering the smart home" - vendor and technology agnostic open source home automation