Line 6's Gearbox Software was the start of their venture into software versions of their amp and pedal simulations, and although the product is mostly discontinued, it still is valuable to computer users today. The sounds in the Gearbox suites are identical to the sounds found in the newer POD Farm suites. The fx include gates, volume pedal, wah pedal, stompbox pedals, delay pedals, modulation pedals, distortion pedals, compressions, eq effects, and reverb effects. Of course, it also includes Line 6's legendary amp and cabinet and microphone modeling, and depending on what version of Gearbox you own (Silver or Gold), you can have anywhere from 18 to 78 guitar amp models. That is quite a lot!
One of the newer features of Gearbox, is that if purchased, you can use the VST or RTAS plugin versions of the Gearbox software. Initially, Gearbox was a standalone executable program, that let you record wet/processed tones into whatever DAW you were using. Now, with the plugin, you can record guitar parts dry, and add the effects and modeling afterwards: this allows much more flexibility, more tweaking power, and much more creative possibilities. However, the guitar amp emulations can be cpu intensive (this is also true with the newer POD Farm software). So using a Gearbox plugin on every track (including vocals) can slow your computer's performance, and you can quickly get CPU overload and glitching. So be careful.
The Gearbox software allows semi-custom routing, where you can change the position of certain effects, like delay or modulation, to be before or after the amp modeling. You cannot, however, use two delays, use two stompbox effects, or do any dual amping: these routing flexibilities were added in the POD Farm software systems. But Overall, Line 6 Gearbox is an incredible piece of software, and if you can get it for free with your Line 6 hardware, it is certainly worth using today.
The software works really well. It performs really well. Very god stability.
I've been using it for two months..
I really like the simplicity of the software, even if the interface is not as nice and clean as that of Native Instruments...It's evidently less good, but it is still intuitive.
Another good point is the online access, you have access to courses, audio material, sheet music and preset banks. It's a great advantage in relation to Guitar Rig 2, for example.
I don't like so much its audio performance. True, it has the same effects as Pod 2, but it's less precise than Guitar Rig 2. Your guitar loses a bit of personality, which is something that doesn't happen with GR 2.
In short, I chose GearBox because I really love the TonePort UX2 but I must admit that I don't use it much. I'm a fan of Guitar Rig 2, which is indeed a bit more expensive, but also better in all respects.