After more than two years FlorisBoard (an open-source keyboard which respects your privacy) 0.4.0 is finally released with many new features including MDY support, addons store, incognito mode, major smartbar rework and many other bugfixes and improvements.

Regarding the spell checking (from GitHub release notes):

Word suggestions/spell checking are not included in the current releases and are a major goal for the v0.5 milestone.