From http://www.openbsd.org/policy.htmlThe original Apache license was similar to the Berkeley license, but source code published under version 2 of the Apache license is subject to additional restrictions and cannot be included into OpenBSD.This rationale mentions additional restrictions but doesn't say what they are. What were the reasons for declaring the Apache 2.0 license incompatible with OpenBSD policy?
Why are Apache 2.0 works excluded from OpenBSD?
licensing;history;apache license;bsd
A few criticisms I found on the mailing list:It's too complex / hard to understand for non lawyersThe copyright notice requirements are annoyingThe patent provisions make the license non freeIt's worse than the previous license.From: Henning Brauer (lists-openbsdbsws.de)  Date: Thu Feb 19 2004 - 02:58:21 CSTthe point is that more and more free software is slowly getting unfree,    more restrictive, etc, and that is not something we should just    passively watch.    please have a look at the new apache license.    it is not really parsable without consulting a lawyer, and as this    license seems to go into the contract law land, the lawyers answer    migth very well be a differing depending on in which country you are.From: Steve (steveszmidt.org)  Date: Mon Jun 07 2004 - 13:59:03 CDTYes indeed. Reading the Apache 2.0 license, it demands notices to be placed in    any modified versions that you distribute. BAAD! It even have the gall to demand that if you prepare Derivative Works, to    carry prominent notices stating that You changed the files. Including    original copyright notices and stuff. This is truly evil. Besides being so nasty it's a really easy to read license for any layman.    Guess they figured that if anyone can read and understand it they will stay    away from Apache. To cap it off, unless you explicitly state otherwise, any contribution    intentionally submitted, will follow the same license! So now others in    their turn also have to include notices and so on. This is a truly unfriendly    license...From: Theo de Raadt (deraadtcvs.openbsd.org)  Date: Fri Feb 20 2004No sorry, the Patent clause seems to give extra rights: the right not     to be sued by a contributor for using their code, so in that sense     the extra length does seem to make the licence more free. That's funny; I cannot see any such thing being covered by copyright  law. As you may know, copyright law only allows you to keep or grant  away the rights covered by copyright law. And since this is a right  not discussed in copyright law, good god, it must not be a valid  copyright term. There has been a load of knee-jerk nonsense from people who clearly     can't (or don't want to) read, asserting that this removes users     rights to sue. It doesn't, it merely removes rights if they sue that     they would never have had under a BSD licence in the first place. Balony. What bothers me is a bunch of OpenBSD folks going over to Apache     licensing lists making assertions that clauses like the patent clause     make the license inherently less free based on poor analysis. It is not free. There is no such thing as a right to not be sued.