Active Directory and MS SQL Server are both solid products, as is .NET. The windows NT kernel is very well thought out, too. The last iteration of windows phone was quite good, if too little too late.
Don't get me wrong, MS will enshitify anything it can to make a quick buck. They're much like Disney in that regard.
SQL Server is a fork of Sybase. Not a MS invention.
Active Directory is probably based on someone's LDAP server, though I don't know for sure.
.NET is a copy of Java
NT kernel is good, thank Digital/Dave Cutler for that.