Silex

Silex is an open-source web builder owned and maintained by the OW2 foundation, a nonprofit that guarantees the project stays freely available. It outputs clean, standards-based HTML and CSS files with no proprietary code hiding inside. You can host the Silex editor yourself or use their public instance, and your exported sites work anywhere HTML runs.

It's ideal if vendor lock-in worries you or if you need a builder that respects software freedom. The long track record since 2007 shows it's stable and battle-tested, appealing to people who value open-source principles and want a tool that won't disappear behind a paywall.