Sony ACID Pro 7 is a powerful pro-level DAW (digital audio workstation) package for music creation.
Neither the feature set nor the price are for amateurs - but if you're serious about making and mixing music, this is one of the DAW programs to consider.
Coming from a loop-based (using repeating sample files to create songs) background, Sony ACID Pro 7 takes a slightly different approach from heavyweights Steinberg's Cubase and Cakewalk's Sonar which started life as MIDI sequencers.
If you're working with and recording audio snippets, you might prefer Sony ACID Pro 7. If you use MIDI and record continuous performances, you might go for one of the latter programs.
Sony ACID Pro 7's feature list is far too extensive to list here, but the major capabilities include tons of loop-based music creation editing tools, multi-track audio recording and midi sequencing (including support for VSTi virtual instruments), video tracking, multiple bus output and inline track editing. If you don't know what all those are, you might check out some less expensive music software first.
We don't like to register names more than we have to, and don't appreciate the trial version of Sony ACID Pro 7's insistence on performing said procedure before using the program.