Is Spring.NET project dead?
Despite having a dead website, nor being listed at spring.io, there is still (in 2015 at least) development activity at JIRA and GitHub.
It appears development continues in spring-net-futures, but there's only one person. As far as production usage goes I'd say it's dead now, but it might come back at some point.
Last commit there was Nov 2017. It's certainly dead now.
Activity started again in the original repo, but only ten commits in the last year (as of June 2020).
I found this question after doing a Google search for "spring.net", following the top link to springframework.net, and seeing the last news update is dated December 11th, 2012.
It looks like the project was resuscitated in September of 2018. The GitHub home page now shows version 3.0.0 (Prerelease) supporting .Net 4.5.2 and .Net Standard 2.0.
Unfortunately, I can't seem to find that version on nuget.org at this point, so from the point of view of a consuming developer it remains effectively dead.