ChaCha20: used in chacha20-poly1305 in TLS, OpenSSH; arc4random in the BSDs, Linux /dev/urandom since 4.8.
Ietf: IETF RFC 7539. Longer nonce, short block counter.
XChaCha20: constructed analogously to XSalsa20; a mixing step during initialization allows using a long nonce and along with a full-sized block counter.
ChaCha12, ChaCha8: faster; lower security margin of safety.