The Steam and DRM free version (directly from Bare Mettle site) are currently the same. Updates are released when they are ready and not on a set schedule (roughly every few months a rather significant content update is released with smaller patches/fixes in between those). Multi-player currently isn't a high priority and will likely be added after the main game content and features are finished.
There isn't a roadmap for releases but if you check the Announcements sub-forum, the Update & Release Notes sub-forum and the What's Next pinned thread then you'll have a good idea about what is going on.