nuBuilder 4 will be released in the next few days.
But here are some links now.
Files on Github - https://github.com/nuSoftware/nuBuilder4
Our first video - https://www.youtube.com/watch?time_continue=1&v=tdh9ILCUAco
There is no upgrade path from version 3 to version 4.
As a small team, we have been focused on other priorities.
But...
Version 3 and version 4 can live in that same database as their system files either start with zzzsys_ or zzzzsys_ and all reports designed with version 3 can be cut and pasted into version 4 as they use the same JSON object.