LSTM or other RNN package for R
Have a look at the rnn package (full disclosure, I am the author). It implements a multilayer RNN, GRU, and LSTM directly in R, i.e. not an underlying C++ library, so you should also be able to read the code and understand what is going on.

install.packages('rnn')


The CRAN version is quite up to date, but the GitHub version is bleeding edge and can be installed using:

if (!require('devtools')) install.packages('devtools')
devtools::install_github('bquast/rnn')