First the commercial ones....

Iona Orbix (C++)
        Orbix v. 2.3c on UW 7.0.1, UW 2.1.2
        Orbix v. 3 not yet in QA process for SCO platforms
        http://www.iona.com

Iona OrbixWeb (Java)
        OrbixWeb v. 3.1 on JDK 1.1.3u
        Later versions on JDK 1.1.7A under test

PeerLogic (ex-ICL) DAIS on UW 7
        (the only ORB officially released for UW 7)
        http://www.peerlogic.com/products/dais/f_dais.htm
        also DAIS J2 for JDK 1.1.x

Inprise VisiBroker, as part of UW7 Netscape Enterprise
        ORB is exposed via IIOP interface

Inprise VisiBroker for Java on JDK 1.1.5 or higher
        http://www.inprise.com/visibroker

Expersoft CORBAplus, Java Edition on JDK 1.1.x
        http://www.expersoft.com


Now some freeware ones....

OmniORB2 v. 2.5.0 on Skunkware 98 for OSR5
        we are trying to get better threading with v. 2.7.0

Chorus COOL-ORB
        once on OSR5, now discontinued?

MICO

ILU     ftp://ftp.parc.xerox.com/pub/ilu

Corbus  http://www.bbn.com/products/dpom/corbus.htm

Electra http://www.olsen.ch/~maffeis/electra.html