Volti is described as 'GTK+ application for controlling audio volume from system tray/notification area' and is an app in the audio & music category. There are more than 10 alternatives to Volti for Windows, Linux, Mac and Windows S. The best alternative is EarTrumpet, which is both free and Open Source. Other great apps like Volti are Volume2, Volwheel, Volume Scroller and Audio Sliders.
Volume2 is an advanced Windows audio mixer, a complete replacement for the standard Volume Control. This application lets you easily change the sound volume just by rotating the mouse wheel or by using keyboard hot keys or just mouse move on screen border.
VolWheel is a little application which lets you control the sound volume easily through a tray icon you can scroll on. It is written in Perl/Gtk2 and works both for ALSA and OSS. You can configure it quickly through its configuration interface.
Volctl - Volume Control per application from System Tray for Linux
Volctl is a free and opensource app for Linux writen in python and gtk+ and that can be used to control volume per application and for enabled pulseaudio outputs from the system tray.