I don't know of any software that does a good job correcting grammar. Computers are not very good at correcting grammar errors in complex, real-world language. If you're making very blatant mistakes in very simple sentences (e.g. if you want to write "the cat is big" and you write "the cat are big") then sure, a computer will catch that...but anything more complex and the computers can be easily confused and give you incorrect advice. The best way to improve your grammar is not to rely on computers, but to expose yourself to many examples of well-written English and emulate what you see. Practice writing and have your text corrected by competent native speakers (here, or on lang8, etc) instead of computer.