There are tons of altnertive which you can find, online, the thing is photoshop is after all photoshop, no one can compete this great product, as they are spending million on updates and different function, that is why most expensive product in photo eiditor,
Well the top photo editor software which i will suggest you are as follow;.
1) Gimp it is a desktop application which you need to download.
2) Browser based Photoshop Online Free. Which you can use from any browser with internet connection < No hassle of download also its a API of Pixlr,
Hope this give you a clear idea . thanks
