Fontello is described as 'Tool to build custom fonts with icons' and is an website in the os & utilities category. There are more than 25 alternatives to Fontello, not only websites but also apps for a variety of platforms, including Self-Hosted solutions, Mac, Windows and Linux. The best alternative is Font Awesome, which is both free and Open Source. Other great sites and apps similar to Fontello are Flaticon, IcoMoon, Fork Awesome and Fonts For Web.
Fontello is mainly a Font Host but alternatives to it may also be Vector Graphic Apps. Filter by these if you want a narrower list of alternatives or looking for a specific functionality of Fontello.
Futuramo Icons is a system of user interface icons with instant search and tools for size, color, style, swatches. The 16-style matrix makes the web app unique. It is a comprehensive, visually compatible, always expanding professional icon system.