Any computer application you can think of from the 1970s or earlier can be replicated by a device of approximately the specs listed in this topic.

IE: Airplanes, Space Exploration, Differential Equations, Matrix Multiplications, Simulations, Cruise Missiles, Homing Missiles, Firing Computers (aka: aim-bots), RADAR, SONAR, Radio communications, Error-correction codes, Reed-Solomon (aka: reliable communications to the Voyager Probe)

To just give you an incomplete idea of what's possible. So erm... anything you want, really. Yeah, we have faster computers today, but we use most of that computational power for convenience and graphics, rather than like, actually solving problems.

The vast majority of car controls (Air Bags, Tire Pressure Sensors, Electronic Computer timings, Traction Control, Radio, etc. etc.) is built up from cheap (but very reliable) microcontrollers. Industrial control systems that run our factories and precisely perform operations using servos and sensors are also using chips of this caliber.

You might be surprised at what a few MHz and a few kilobytes of RAM can accomplish.