The new Teensy 3.5 is a small, breadboard-friendly development board developed by Paul Stoffregen and PJRC. Teensy 3.5 brings a 32-bit ARM Cortex-M4 platform to hobbyists, students and engineers, using an adapted version of the Arduino IDE (Teensyduino) or programming directly in C language.

Specifications:

• 120 MHz ARM Cortex-M4 with Floating Point Unit
• 512K Flash, 256K RAM, 4K EEPROM
• Microcontroller Chip MK64FX512VMD12 (PDF link)
• 1 CAN Bus Port
• 16 General Purpose DMA Channels
• 5 Volt Tolerance On All Digital I/O Pins
• 62 I/O Pins (42 breadboard friendly)
• 25 Analog Inputs to 2 ADCs with 13 bits resolution
• 2 Analog Outputs (DACs) with 12 bit resolution
• 20 PWM Outputs
• USB Full Speed (12 Mbit/sec) Port
• Ethernet mac, capable of full 100 Mbit/sec speed
• Native (4 bit SDIO) micro SD card port
• I2S Audio Port, 4 Channel Digital Audio Input & Output
• 14 Hardware Timers
• Cryptographic Acceleration Unit
• Random Number Generator
• CRC Computation Unit
• 6 Serial Ports (2 with FIFO & Fast Baud Rates)
• 3 SPI Ports (1 with FIFO)
• 3 I2C Ports
• Real Time Clock

The latest in the line of very powerful, USB-capable microcontrollers, the Teensy 3.5  development board is faster, more capable, and bigger, putting even more pins on a solderless breadboard.

Also available:
Teensy 3.6