I was asked on Quora about NLP approaches or tools to automatically rewrite sentences. Here is my brief answer (feel free to vote on Quora). Also note that I have updated the answer to include seq2seq models.
Not really a specialist in sentence re-writing, but I think at least the following approaches can be used:
1) Manual rules. These can be either regexp based or tree-based. Stanford folks have a tool to create such patterns. One interesting option is to implement rules based on POS tags. I, e.g., reimplemented some of the query-rewriting algorithms from Aranea QA system. This is not easy and the quality is sometimes not ideal.
2) Learned from data. One common approach to do this is, perhaps, surprisingly machine translation. This would require a rather large monolingual corpus of paired sentences. One sentence would be source and another would be a target. You can train all sorts of translation models on such a corpus starting from simplistic Model 1 and ending with some phrase-based model (or even context-free grammar based, see the link below).
3) It is also possible to obtain paraphrasing information by pivoting on a foreign language. Here is one link PPDB: The Paraphrase Database. You may want to read papers authored by the guys who created PPDB.
4) I suspect that even better translation results will be obtained by using synchronous context-free grammars. There is in fact an open-source package that apparently supports all of this: cdec.
5) A more recent approach relies on neural sequence-to-sequence (seq2seq) models. One recent paper on this subject is: Neural Paraphrase Generation with Stacked Residual LSTM Networks, Prakash et al., 2016.