The most powerful Android/Linux computer board which costs less then € 100,- is the Radxa Rock with a quad core processor
Radxa Rock is a single board computer that is based on Rockchip RK3188 processor and is equipped with Bluetooth 4.0, WiFi, LAN, RTC, IR etc. The CPU is ARM Cortex-A9 with quad core at 1.6Ghz, including GPU that support OpenGLES 2.0.This means you can play 1080p videos with HDMI. The Radxa Rock has 8GB flash memory and a dual 40-pin header connector with amongst others, GPIO, I2C, Line in, USB 2.0, PWM, ADC, LCD and GPS interfaces. Read more...

Arduino compatible module with WiFi can be programmed via internet
The Spark Core is an open source microcontroller module with WiFi that has been developed after a successful crowd funding on Kickstarter. The module has ARM Cortex-M3, many I/O possibilities, CC3300 WiFi and can be programmed wireless via Spark Cloud. The Core uses progamming language Wiring, just like Arduino. You can easily connect the Core to the internet using the Spark App. Read more...

Use all sensors and I/O from your smartphone for Arduino
1Sheeld turns your smartphone into a re-configurable shield. 1Sheeld consists of two parts. The first part is a shield that allows for wireless communication with the Android smartphone via Bluetooth. The second part is an app on the smartphone which provides the communication with the shield and which you can use to choose between various available shields. There are shields available for buzzer, keypad, LED, Twitter, Facebook, E-mail, switch, potentiometer, SMS, camera, gyroscope, microphone, accelerometer, etc. Read more...

WIZnet W5500 Ethernet module and shield
The W550 chip is an improved version of the W5100 which is used on the Arduino Ethernet Shield. Compared to the W5100, the W5500 is faster, has a larger buffer, supports 8 sockets, uses less power, is smaller and cheaper. The manufacturer of the chip, WIZnet, has developed a module and a shield. With the new Ethernet library the shield can be easily used for Arduino. Read more...