Grammarly is an easy-to-use program. The grammar check is free, although you have to sign up with the website. Copy and paste your content into the text box and in as little as 10 seconds, Grammarly will analyze your work, send you a detailed report and suggest corrections.
Language Tool is an open-source program. It is not as user-friendly as Grammarly, simply because you must download the program and your computer must meet all the minimum requirements. However, it is superior in its ability to catch mistakes. It features a program called "After the Deadline," a powerful grammar check designed to focus on common mistakes. Language Tool includes other languages in the program, including French, Italian and Spanish.
AbiWord is another open-source program you must download and install onto your computer. It is available for Mac and Windows and is a stand-alone word processor with a built-in grammar check.