The CD4047 is capable of running in astable or monostable configurations, with operating frequency configured by an external RC network. So in one sense, sounds like the 555 timer!

Unlike the 555, the CD4047 provides a fixed 50% duty cycle with good frequency stability (+/- 2% @ 100KHz).

As always, all notes, schematics and code are in the Little Electronics & Arduino Projects repo on GitHub.