+1 to BetterTouchTool! I'm mostly a keyboard person (typical 'vim' user etc.) but being able to switch tabs using a two-finger tap left and right on the touchpad is so pleasant that I find it worth the investment for BetterTouchTool alone. Configuring this for the different keybindings of different programs flexibly is really great. And it's a one-time payment including fixes and improvements - I've had it for years.

+1, I can't live without BTT on Mac. From keyboard shortcuts, window management, controlling apps, overall customizations, HUD messages, and much, much more.

I wish BTT were multi-OS, so I could just copy the configuration across platforms, instead of having to recreate from scratch (Linux), or not at all (ChromeOS).