a 74HCT240 Will oscillate 1 section or many If the inputs are open usually at about 30-60 MHZ. They get real hot and without a scope are really difficult to separate from a shorted output, Add a crystal and a telegraph key and you have a 1/2 watt transmitter. One section for the oscillator one as a buffer and 4 in parallel for the "Power Amp" there was a write up in the ARRL handbook (Great way to learn basic electronics from the ground up) in the early 2000's. As MarkT pointed out an open input is not really a good thing to have. I've always grounded the inputs as ground is usually the easiest thing to find when laying out a PCB. If one makes sure that unused pins are set to output and low there is no issue possible that could really cause damage except as pointed out for Low Current applications.
Bob