To install LibreOffice on Solaris x64 platform you have to add software repository to your system and then install LibreOffice. OpenIndiana users may need the workaround mentioned here: http://sfe.opencsw.org/workbench-2017-01 and replace every "s11" with "oih".

For Solaris 11.x:
To register a new repository you have to execute as a power user this command:
pkg set-publisher -G '*' -g http://sfe.opencsw.org/localhosts11 localhosts11

For Solaris 11.4 beta (was: Solaris 12 in development (*))
To register a new repository you have to execute as a power user this command:
pkg set-publisher -G '*' -g http://sfe.opencsw.org/localhosts12 localhosts12

When your repository is ready you can install LibreOffice,
LibreOffice 4.4.x comes in 2 packages: libreoffice4 libreoffice4-desktop-int
LibreOffice 5.2.x comes in 2 packages: libreoffice52 libreoffice52-desktop-int

Choose the version you would like to install and then run command

For LibreOffice 5.2.x you have to execute:
pkg install -v libreoffice52 libreoffice52-desktop-int

For LibreOffice 4.4.x you have to execute:
pkg install -v libreoffice4 libreoffice4-desktop-int

During the installation pkg will install all necessary libraries and other packages.

Here is a complete example how LibreOffice 5.2 was installed on Solaris 11.3 desktop:
pkg install -v libreoffice52 libreoffice52-desktop-int
Packages to install: 6
Mediators to change: 1
Services to change: 2
Estimated space available: 934.34 GB
Estimated space to be consumed: 1.68 GB
Create boot environment: No
Create backup boot environment: No
Rebuild boot archive: No

Changed mediators:
mediator libreoffice:
version: None -> 5.2 (system default)

Changed packages:
localhosts11
desktop/application/libreoffice52
None -> 5.2.3.3,5.11-0.0.175.3.1.0.5.0:20170103T191502Z
desktop/application/libreoffice52-desktop-int
None -> 5.2.3.3,5.11-0.0.175.3.1.0.5.0:20170103T192726Z
sfe/library/g++/libcdr
None -> 0.1.3,5.11-0.0.175.3.1.0.5.0:20161224T143401Z
sfe/library/g++/libixion-011
None -> 0.11.1,5.11-0.0.175.3.1.0.5.0:20161224T135901Z
sfe/library/g++/liborcus-011
None -> 0.11.2,5.11-0.0.175.3.1.0.5.0:20161224T142803Z
sfe/library/mdds-12
None -> 1.2.2,5.11-0.0.175.3.1.0.5.0:20161224T135236Z

Services:
restart_fmri:
svc:/application/desktop-cache/desktop-mime-cache:default
svc:/application/desktop-cache/mime-types-cache:default

DOWNLOAD PKGS FILES XFER (MB) SPEED
Completed 6/6 14652/14652 258.9/258.9 1.8M/s

PHASE ITEMS
Installing new actions 15387/15387
Updating package state database Done
Updating package cache 0/0
Updating image state Done
Creating fast lookup database Done
Reading search index Done
Updating search index 6/6
Updating package cache 5/5


If the installation process fails because of the network issues
DOWNLOAD PKGS FILES XFER (MB) SPEED
desktop/application/libreoffice52 0/6 10865/14652 211.0/258.9 151k/s

Errors were encountered while attempting to retrieve package or file data for
the requested operation.
Details follow:
http protocol error: code: 500 reason: Internal Server Error
URL: 'http://sfe.opencsw.org/localhosts11/file/1/83755365f1790a7413e5523b6b0a64123d5b8c5a'


then you have to re-run the command and it will continue from where it stopped.

When LibreOffice is installed you can start it either from your desktop launch menu Applications -> Office -> LibreOffice 5.2 or you can start it as /usr/lib/libreoffice5.2/program/soffice from your terminal window.

You can check for the latest updates by executing these commands:
pkg refresh
pkg update -nv

If there are updates available:
pkg update -nv
Packages to update: 2
Services to change: 1
Estimated space available: 934.00 GB
Estimated space to be consumed: 816.26 MB
Create boot environment: No
Create backup boot environment: Yes
Rebuild boot archive: No

Changed packages:
localhosts11
desktop/application/libreoffice52
5.2.3.3,5.11-0.0.175.3.1.0.5.0:20170103T191502Z -> 5.2.4.2,5.11-0.0.175.3.1.0.5.0:20170107T191831Z
desktop/application/libreoffice52-desktop-int
5.2.3.3,5.11-0.0.175.3.1.0.5.0:20170103T192726Z -> 5.2.4.2,5.11-0.0.175.3.1.0.5.0:20170107T192237Z

Services:
restart_fmri:
svc:/application/desktop-cache/mime-types-cache:default


then you can install the updated version
pkg update -v
Packages to update: 2
Services to change: 1
Estimated space available: 933.68 GB
Estimated space to be consumed: 816.26 MB
Create boot environment: No
Create backup boot environment: Yes
Rebuild boot archive: No

Changed packages:
localhosts11
desktop/application/libreoffice52
5.2.3.3,5.11-0.0.175.3.1.0.5.0:20170103T191502Z -> 5.2.4.2,5.11-0.0.175.3.1.0.5.0:20170107T191831Z
desktop/application/libreoffice52-desktop-int
5.2.3.3,5.11-0.0.175.3.1.0.5.0:20170103T192726Z -> 5.2.4.2,5.11-0.0.175.3.1.0.5.0:20170107T192237Z

Services:
restart_fmri:
svc:/application/desktop-cache/mime-types-cache:default

DOWNLOAD PKGS FILES XFER (MB) SPEED
Completed 2/2 3544/3544 100.5/100.5 4.8M/s

PHASE ITEMS
Installing new actions 95/95
Updating modified actions 3456/3456
Updating package state database Done
Updating package cache 2/2
Updating image state Done
Creating fast lookup database Done
Reading search index Done
Updating search index 2/2
Updating package cache 5/5

---------------------------------------------------------------------------
NOTE: Please review release notes posted at:
https://support.oracle.com/rs?type=doc&id=2045311.1
---------------------------------------------------------------------------


Please visit http://sfe.opencsw.org/quickrepolinks for more information about other repositories

(*) Solaris 12 is not released yet and LibreOffice might not be production ready for this OS.
Use it with caution.
Note: Solaris is a Trademark of Oracle. "Solaris 12" is just a working title and if you google a bit around, you'll see that the Solaris Release model has change to a continuos mode, what is indeed a very good idea in my personal view (tomww). So next we might see new cool features under the name Solaris 11.4 instead of the name Solaris 12.

Originally posted 20170109
Edit: 20170205 add link to OpenIndiana workaround (tomww)
Edit: 20170207 add hint to replace "s11" with "oih" for OpenIndana Hipster. (tomww)
Edit: 20170403 Add Note about the working title "Solaris 12" (tomww)
Edit: 20180131 add new Name: Solaris 11.4 beta (tomww)