Seq24 is described as 'minimal loop based midi sequencer' and is an app in the Audio & Music category. There are more than 10 alternatives to Seq24 for a variety of platforms, including Windows, Mac, Linux, BSD and Windows Phone. The best alternative is LMMS, which is both free and Open Source. Other great apps like Seq24 are FL Studio (Paid), Reaper (Paid), Ableton Live (Paid) and Bitwig Studio (Paid).
FL Studio (originally known as FruityLoops) is a full-featured Digital Audio Workstation (DAW) offering a complete range of professional tools for everything from audio editing and beat creation to advanced arrangement, composition, mixing and mastering.
Reason is a virtual studio rack with all the tools and instruments you need to turn your ideas into music. And it's more than just a set of excellent synths and effects. It's a complete music system. Step into the age of Reason.