Mockup Builder is not available for Linux but there are plenty of alternatives that runs on Linux with similar functionality. The best Linux alternative is Pencil Project, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 25 alternatives to Mockup Builder and 12 are available for Linux so hopefully you can find a suitable replacement. Other interesting Linux alternatives to Mockup Builder are quickMockup (Free, Open Source), mydraft.cc (Free, Open Source), WireframeSketcher (Paid) and Wirify (Freemium).
Online tool for creating mockups in the browser. Use your browser’s save function to save the file (just html for view only, complete save for an editable version) or export to codepen for others to view.
WireframeSketcher is a software tool that helps quickly create wireframes, mockups and prototypes for desktop, web and mobile applications. It comes both as a plug-in for any Eclipse-based IDE and a standalone version.
UXPin is a web-based system for managing design documents like wireframes, sitemaps, persona descriptions or flowcharts. It lets you upload image files, invite teammates to review and comment on them, and keep track of revisions.
HotGloo is a UX, wireframe and prototyping tool designed to build wireframes for web, mobile and wearables. Create and share fully interactive prototypes with your team and clients and gather feedback on the process.