Photo metadata. Keywords, description / caption:

ExifRenamer (have)

http://itunes.apple.com/us/app/ingestamatic/id476718466?mt=12

Straight-up iPhoto competitors:

http://www.kavasoft.com/Shoebox/ [This has gone the way of the cloud. Boo!]

http://www.lynapp.com/index.html

[added 2015-01-23]
http://www.pixa-app.com

Too bad UPnP / DLNA is such a shambles. Network photo streaming is where iPhoto has [had] them all beat… so long as you connect via OS X, iOS, or TV. [Sharing iPhoto to iPhoto has been removed. You’re supposed to rely on iCloud photostream sharing. This “solution” is ass.]