the end of desktop apps (picasa, Windows Photo Gallery). Choose a free app (with open source), freeware? Example of image organizer, photo editor and photo sharing service.

Microsoft announced that Windows Photo Gallery will no longer be supported or be made for download after January 10, 2017.
Google announced that Picasa will no longer be supported or be made for download after March 15, 2016.
They said "focusing on the cloud-based Google Photos or one drive"...
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We still need a desktop image organizer & photo editor with touch-up abilities (not strictly viewers).

A comparison:

https://en.wikipedia.org/wiki/Image_organizer
http://www.photosorting.com/

few image organizers with photo edition by build-in features.

Some desktop image softwares (open source and cross-platform):

-https://www.digikam.org/

• free and open source (and binaries for windows, macOSX, linux, unix)
• decorate is too simple (insert text with only some rotations 90°,180°),
• no manual corrections (as local blur)

-https://krita.org/en/download/krita-desktop/

• Krita is a free and open source painting tool designed for concept artists, illustrators, matte and texture artists, and the VFX industry. 
• binaries for windows, macOSX, linux

-http://nomacs.org/
nomacs is a free, open source image viewer, which supports multiple platforms (mac (with mac port), linux windows).It is able to browse images in zip or MS Office files which can be extracted to a directory.
if you are frequently using Matlab and you want the image sync functionality of nomacs, you can download this Matlab script and add it to your Matlab folder. Matlab images can then be displayed by typing:
>> nomacs(myImg, []);
BAD: editing an image is too poor.

freeware windows and MAC)

JetPhoto Studio 
http://www.jetphotosoft.com/web/home/
Good: Users can review photos on a map showing the locations where each shot was taken. JetPhoto matches digital photos with time-synchronized GPS tracks to locate photos automatically.
Present photos on Google Earth and Google Maps
Now launch 'Google Earth' which displays the locations of all these GPS-located photos or package both the photo files and GPS tracks into one KMZ file that can be shared easily and opened with Google Earth anytime later!

JetPhoto Studio also gives you the ability to easily generate a web gallery and link all your GPS located photos on a Google Map!

Uses Google Maps API v3.

http://www.jetphotosoft.com/gmap/demo_list.gmap/
http://www.jetphotosoft.com/gmap/demo_jpstudio5.gmap/

BAD: editing an image is too poor.

freeware  (windows)

the best:
http://www.irfanview.com/
Only windows, fast program, some plugins
also:
-http://www.faststone.org/FSViewerDetail.htm

-http://www.xnview.com/en/xnviewmp/
Multi-Platform, organiser, media browser, viewer,
the program is an excellent viewer but almost useless for photo sorting
no manual correction, no text tool...

Ref:
https://www.netdiggers.com/picasa-alternatives/
https://www.cnet.com/how-to/comparing-the-best-ways-to-store-your-photos-online/
https://www.cloudswave.com/socia-media/s/flickr-pro/compare/phanfare-vs-smugmug-premium-vs-zenfolio/
https://blogs.esri.com/esri/arcgis/2016/09/13/story-maps-and-picasa/
http://www.idownloadblog.com/2016/01/16/best-cloud-photo-storage-iphone/

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Online w/ App

-https://pixlr.com/
only photo editor,
and desktop apps:
multi-platform (windows, mac, mobile ios android,web app).

-http://www.sumopaint.com/
web app

https://www.befunky.com/
3 web apps

https://www.picmonkey.com/
4 web apps

https://picsart.com/
iOS, Android, and Windows and web app.

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freeware/shareware
http://www.picajet.com/en/index.php?page=features


PS:
Graphicsmagick is used to process billions of files at the world's largest photo sites (e.g. Flickr and Etsy).
-http://www.graphicsmagick.org/
(free and open source)