It's long-since been rewritten. Pre-SQL Server 2000 it was garbage, but it's been improved significantly since then. I'd still use alternatives given the choice, but it's a solid DB.

>Active Directory is probably based on someone's LDAP server, though I don't know for sure.

So you don't know. It was written in house, using a bunch of standardized protocols (LDAP, X.500, kerberos), though with proprietary extensions (GPOs, etc).

> .NET is a copy of Java

That's a gross oversimplification. It's arguably a rip-off after MS tried to sabotage java, but it's their own implementation.

> NT kernel is good, thank Digital/Dave Cutler for that.

Yes, MS hired an experienced OS person for it. Probably one of the best things they ever did.

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I'm not saying MS deserves kudos or the benefit of the doubt, but they can put out good software, and these are all mission-critical examples of what they have to (having AD go down would bring a whole corporation to a halt). The problem is that with almost everything else, MS has the incentive and capability to ruin. And ruin they do...