It wasn't free, in fact Adobe wanted $99 which is almost as much as the upgrade to CS for it. After CS came out they discontinued it.
The addin gave RAW and JPEG2000 support. Since discontinuation I don't think you can even upgrade it to the latest cameras (but I am not sure of this)
This was in the original documentation for the plugin
Note: The Adobe Photoshop Camera Raw plug-in will be included as part of a future version of Adobe Photoshop. Adobe does not promise the long-term availability of this plug-in for standalone purchase. Your purchase of the plug-in does not entitle you to discounts on future upgrades of Photoshop.
Also FYI
Supported cameras
Canon
EOS-1D
EOS-1Ds
EOS-D30
EOS-D60
PowerShot 600
PowerShot A5
PowerShot A50
PowerShot S30
PowerShot S40
PowerShot S45
PowerShot G1
PowerShot G2
PowerShot G3
PowerShot Pro70
PowerShot Pro90 IS
Fujifilm
FinePix S2 Pro
Minolta
DiMAGE 5
DiMAGE 7
DiMAGE 7i
DiMAGE 7Hi
Nikon
D1
D1H
D1X
D100
Coolpix 5700
Coolpix 5000 — with firmware version 1.7
Olympus
E-10
E-20
C-5050 Zoom
No I don't have a copy of it, I just did a search for it earlier before I gave up and got the upgrade to CS. Since CS gives a lot more 16 bit functions it was worth it.