Pixlr is a free tool for editing photos. You can crop, resize, add filters and stickers, and more. There is also a pixlr mobile app that will allow you to edit photos right from your phone.
Want to create the perfect profile pic? Try Canva. It's completely free and not just for pictures! You to create all kinds of fun, professional looking documents and presentations (including presentations and resumes) for free. Canva does charge for some of their options and images, but you can make a great project without paying a cent.
BeFunky offers a huge selection of photo editing options including a collage maker and a way to cartoon-ify your photos! It's free to use, but does have ads.