On of the most universal timer circuit which finds its ways into so many applications and projects, the 555 was introduced by Signetics in 1972.
You can apply it to timers, oscillators, monoshots, pulse generators, etc. In case you need 2 timers in a single package you can go for the 556 or the 558 for a quad device package.
The internal circuit of a 555 IC is shown below:
To make an astable multivibrator you can use the simple circuit below:
The waveform generated is as below:
You can choose C, R1, R2 values as below: