Mersenne Twister MT19937
Pseudorandom number generator from 1997 by Makoto Matsumoto and Takuji Nishimura. Its period is 219937−1 — a Mersenne prime, hence the name.
Became the default generator in practically everything: Python (random), Ruby, PHP, R, MATLAB, Excel. Fast, well distributed and thoroughly vetted by statistical test suites. But it is not cryptographically secure — 624 observed outputs are enough to reconstruct the entire internal state and predict the rest. Use secrets / /dev/urandom for anything involving keys or tokens. Newer languages have moved on to PCG (NumPy since 2019) and xoshiro/xoroshiro, which are faster and carry less state.