I demoed L3 and it sounded OK. Some posters on prosoundweb reported that it sounds more analog than their analog devices:) However I still like the combination of LinMB and L2 more, probably because I am used to this.
The other software only options (considering what L3 does I am giving you list of Multiband Dynamic processors, EQs dedicated to mastering (mostly "linear") and Limiters...)for OSX are:
-Ozone3 from izotope (some users here reported that it is very good)
-The CQ1 Multi-Band Compander and The DQ1 Dynamic Equaliser from Sonalksis
I did not test any of those. From my research on the prosoundweb forums I can say that theese two (Izotope and Sonalksis) are not considered as the highest quality mastering tools (as Waves or TC 6000 stuff)
Then there are plugins for which ou need a PCI (PCI-X or PCI express available) cards:
UAD-1 with their Mastering tools: (available separately)
http://my.uaudio.com/store/productinfo.php?cPath=22&productsid=47&osCsid=29b2068ce2052ffc584d2d37c2fabdfe
UAD precision limiter has a very good reviews and it is quite often recommended by well known (or trustable) guys from prosoundweb. It is probably even more popular than Waves limiters (L2, L3) (some people do not like L2 at all!)
Finaly TC Powercore mkII which has more options (three band multiband comp is included, five band as optional... some limiter included, some optional...)
They´re offering MD3 Stereo Mastering package which is derived from their superb TC6000 Mastering system.
http://www.tcelectronic.com/MD3PowerCore
This solution is more expensive than UAD-1 with their Mastering bundle but I can not say which one is better, as I don´t know 😟
Than there is a Sony Oxford Limiter,( with one of best reviews around) but you have to have a Pro Tools TDM rig (maybe a Mix card is enough-I do not know...some SonyOxford plugins are available for TC Powercore - like Inflator, which could interest you too. Unfortunately the SonyOxford Limiter is not available for Powercore...)
Personally I am now decieding which direction I go...
As I said I am familiar with LinMB and L2 from Waves (from my ex Windoze life) and working with theese is very easy for me. On the other hand it would be nice to have a DSP card and in that case the UAD-1 is the favorite for the price and reported quality of plugins. But I can not say nothing against the TC also- I have only good experiences with their hardware stuff (and also with their already discontinued Native Bundle of plugins) and they have perfect customer support. AND finally there is a possibility to have APA card from Waves which saves CPU so I really do not know yet...