The developer of optimFROG has released version 4.6000ex, an experimental version with a variety of improvements.
optimFROG 4.6000ex
New Features

the highnew, extranew, bestnew modes and –maximumcompression get slightly better compression (on average 0.1%)

added –experimental option, enabling advanced experimental compression, which is NOT backward compatible with any previous 4.5xx versions

use –experimental with any mode for greatly improved […]

A new version of OptimFROG has been released as well as a new SDK (1.210b). Future development
What is new in this version 4.520b:

successfully ported to Linux/amd64 as well as Darwin/ppc (PowerPC G3)

many internal source code improvements

all the newly created compressed files are completely backwards compatible (can be […]

On Dec. 16th 2001 OptimFROG 4.0b was released into the world providing at the time, the best lossless compression available.
The upcoming release of OptimFROG due out in the next few weeks will have the following features:

significantly improved compression [done, integrating into mainstream OFR]
creation of self extracting archives, 30kB only SFX code for Windows [90%]
ID3v2 tags […]