Emerald clones Phoenix and Emergence are now approved. Linden Labs third party viewers. These viewers have much of the same functionality as Emerald, some are saying Phoenix comes closest to what Emerald was, but I have not used either and cannot comment. You will not be able to use Emerald after 10:00 a.m. tomorrow SL Time.
I recommend you try both and see which one you like.
Here are the Linden download links:
Linden Lab's page for the Emergence Viewer: http://viewerdirectory.secondlife.com/listing/show/listing_id/203
Web Site: (Note: not working as of 7:30 PM on my computer): http://emergence.covenantrealm.com/
Linden Lab's page for the Phoenix Viewer: http://viewerdirectory.secondlife.com/listing/show/listing_id/209
Web Site: http://www.phoenixviewer.com/
In addition there is a new approved viewer today, Ascent, for content creators that I do not know much about. I will report back once I use it.
Linden Lab's page for the Ascent Viewer: http://viewerdirectory.secondlife.com/listing/show/listing_id/208
Web Site: http://ascent.balseraph.org/
I have become used to Imprudence in the past two weeks, I will be testing all of these for photography and will let you know my findings.