Aviary is one of the most used tool on the web free to edit and modify images, from very little available for devices Android bringing a good alternative to paid applications as the Adobe suite .
The editor has many effects, camera filters and options available for easy editing of images directly from smartphones and tablets: these are obviously the classic tools for adjusting brightness, contrast and red-eye and the ability to insert drawings and text for complete customization.
The only oddity is that the Aviary Photo Editor can not currently be initiated by one : in fact, need to make use of the image display to edit and open the options for sharing, you can choose from there just Aviary.
The application is free but as mentioned poses some limitations in the tools and effects that can be purchased separately if they feel the need. Download from PlayStore.