Grammar Bytes! is a site created by Robin L. Simmons, who's a woman, but that's all I know about her. On the site you'll find:
- detailed definitions of common grammar terms
- exercises to test your grammar knowledge
- teacher handouts that accompany the interactive exercises
- tips and rules
The site is well-designed with a nice chunky feel to it. Not all of the grammar exercises will be of interest to EFL learners (e.g. comma splices and fused sentences!) but there's plenty of useful material here for those who want to work on this area of their English.