The best open source alternative to Avocode is Akira, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 25 alternatives to Avocode and four of them is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to Avocode are Mockplus iDoc (Freemium, Open Source), Sketch Measure (Free, Open Source) and Marketch (Free, Open Source).
Mockplus idoc is an online design collaboration tool for digital product teams, including designers and engineers. It connects your design work from design to development and helps teams with design handoff.