Nucleo is described as 'beautiful library of 29280 icons, and a powerful application to collect, customize and export all your icons'. There are more than 25 alternatives to Nucleo for a variety of platforms, including Online / Web-based, Mac, Windows, Self-Hosted solutions and Linux. The best alternative is Font Awesome, which is both free and Open Source. Other great apps like Nucleo are Flaticon (Freemium), Fontello (Free, Open Source), IcoMoon (Freemium, Open Source) and Fork Awesome (Free, Open Source).
Fork Awesome is now a community effort based on Font Awesome by Dave Gandy. We love Font Awesome but here's why we forked it into Fork Awesome 1.1. One Font, 744 Icons In a single collection, Fork Awesome is a pictographic language of web-related actions.
Iconset is a free, powerful and fast SVG icon organizer and manager for designers A minimal app to collect, customize, share and manage all your SVG icon sets in one place. Icons Organizing Organize all of your SVG icons with icon sets, groups and tags.