Long short-term memories ("LSTMs": Hochreiter and Schmidhuber (1997)), a particular variant of RNN, have become particularly popular, and been successfully applied to a large number of tasks: speech recognition (Graves et al., 2013), sequence tagging (Huang et al., 2015), document categorisation (Yang et al., 2016), and machine translation .
as pointed out by  and Linzen et al.