Herbert Dingfelder known as DL5NEG among radio amateurs have constructed a microcontroller based frequency counter up to 70MHz.

Frequency counter can use prescalers what allows reading GHz with 10kHz resolution. Without prescaler device can measure frequency up to 70MHz with 10Hz resolution. I think this is very good what simple schematic can offer. Hex file is ready for download and can be flashed to Atmega16.