As Diki says Alberton Live is a great program, http://www.ableton.com however there is also the stalwart Cubase, http://www.steinberg.net/en/home.html and if you have a Mac, Logic. http://www.apple.com/logicstudio/

If you are looking for arranger software then there is OMB http://www.1manband.nl/omb.htm Livestyler http://www.live-styler.de/home/ and vAarranger http://www.varranger.fr/

If you’re looking for high quality software instruments (VST etc.) then try Komplete 6 http://www.native-instruments.com/#/en/products/producer/komplete-6/ Kore 2 (With or without hardware controller) http://www.native-instruments.com/#/en/products/producer/kore-2/ and Goliath http://www.eastwestsamples.com/details.php?cd_index=1071

A good resource for the above is http://www.synthzone.com/ and for VST also add http://www.kvraudio.com/

There also many modules of Workstations, and players (Ketron http://www.ketron.it/home/index.asp offer good value on the latter)

Enjoy investigating

Bill