With the release of Horde 4 the complete framework has been released as single components. [http://pear.horde.org The Horde PEAR server] offers about a hundred distinct packages by now. Splitting the software in that many components has several benefits. On the one hand it restricts the developers to the boundaries provided by the interfaces offered by the modules. This has a direct effect on code quality. And on the other hand it allows adapting a Horde installation to diverse environments in a very flexible manner.
You may be used to installing a web application by extracting a single tar archive to the document root of your web server. Installing dozens of modules this way would be something that cannot be done manually anymore. A package manager is required. In the PHP world the dominant solution is the PEAR system. While it may not be that widely used and also have some issues it is being present by default on each PHP installation. If your system supports PHP it is unlikely that you do not have PEAR.
Thus the Horde developers decided to support the PEAR system for installing Horde 4 - at least as long as nothing better comes along. In addition PEAR is the only system supported by the developers for installing and updating Horde 4. Providing alternatives would simply consume too much time which is better spent developing the source code.
But of course the Horde developers hope for third parties to repackage the original distribution of PEAR packages. This has a long tradition: Horde 3 has been available as distribution specific packages on nearly all major Linux distributions and it has been repackaged for cPanel and Plesk. The same is happening for Horde 4. You rather want tar archives or would prefer a phar package? Go for it. We will list it here.
+ Horde 4
Horde 4 has not yet been picked up by that many distributions. A few offer it already but we expect the list to grow over time.
* [http://software.opensuse.org/search?q=horde&baseproject=openSUSE%3A12.1&lang=de&exclude_debug=true OpenSUSE]
* [http://www.freebsd.org/cgi/cvsweb.cgi/ports/www/horde4-base/ FreeBSD]
* [http://packages.debian.org/wheezy/php-horde-activesync Debian] (in progress)
+ Horde 3
Horde 3 has been packaged for pretty much all major distributions. It should be no problem to find the corresponding packages.
+ Web hosting management tools
Both [http://www.cpanel.net/ cPanel] and [http://www.parallels.com/de/products/plesk/ Plesk] integrate Horde 3 in the set of web applications that you can install via either of the tools. Both seem to be working on integrating Horde 4. At least for cPanel there is a [http://forums.cpanel.net/f145/horde-groupware-webmail-edition-4-0-case-50766-a-216042.html corresponding thread]
Thus you can use these web application management tools to get a Horde installation with a minimum of fuss. Usually you will loose some of the flexibility you gain with a PEAR or distribution based installation but on the other hand this may reduce potential sources for error.