Patterninja is described as 'lets you easily create tiled patterns online by combining images from an integrated library of predefined graphics or by uploading your own. Produced patterns can be downloaded in high resolution and used for printing and the web'. There are five alternatives to Patterninja, not only websites but also apps for Android, iPhone, Android Tablet and iPad. The best alternative is Adobe Capture, which is free. Other great sites and apps similar to Patterninja are BgPatterns (Free), Patternify (Free), Patternizer (Free) and Pattern Designer (Free).
Patternify lets you easily create, edit and share tiled patterns online. Draw patterns from scratch, load up presets or access pre-made patterns through a special URL feature. Then export the patterns as PNG or as a CSS pattern via Base64 encoding.