One of the most exciting recent developments in the guitar-playing world has been the release of Neural Amp Modeler (NAM), which is an open source project created by programmer Steven Atkinson.
Although akin to the humble amp simulator, of which there have been a plethora over the years, this uses profiling and machine-learning technology just like recent commercial software releases such as IK Multimedia's Tonex and the popular Kemper and QUAD Cortex hardware.
But the major difference here is that the software is completely free, independent and has already inspired a growing community of users to create profiles of their own amps (and other outboard gear such as microphone pre-amps and even guitar pedals!) to share with the world.
Follow this Github link and navigate to the assets and choose your operating system. Make sure the .vst3 file lands in the folder where your VST plugins are stored. Open your DAW (I'm currently using Ableton Live Lite as part of a project I'm currently undertaking - more of which later) and open NAM.
Firstly you will need some profiles - here's a large zip file containing a whole boatload of them to get started with. I also recommend joining the Facebook group where people are constantly sharing new profiles.
You will also need a cabinet impulse response as NAM only models the preamp/power amp section of the amplifier - there is an IR loader built into NAM but if you prefer I can recommend the free IR loader NadIR by STL Tones and tons of cabinet IRs online you can google. I've been using the free version of MIKKO2 from ML Sound Lab which comes with one cabinet and a bunch of mics to get started.
Tip: Make sure you gain-stage properly. Don't send a really hot signal from your interface into NAM - try to aim for around -14dBfs and use the Input dial in NAM to drive the signal like a Gain control on a regular amplifier. Balance the output signal with NAM's Output. I've also found with some profiles you need to back off the Input on NAM a few dB when gain-staging.
I'm still in the process of auditioning the many profiles that are already out there (enjoying the Vox AC15s and one of a Studer tape machine!) and hoping for a Roland Jazz Chorus JC120 at some point- but I'm thoroughly enjoying this community-led project which is quite frankly far too good to be free!