I use a variety of programs depending on what I am trying to achieve and how hard I want to work with it. You can install any of them from Software Center or using apt-get

Audacity - Simple recording and editing. If you are doing a couple of tracks and generating stereo output, this will work.

Rosegarden - This is my bread and butter when I come down to working with MIDI files and doing sequencing. I use a MIDI keyboard for entry, QSynth (fluidsynth) as the playback MIDI device(s), and Rosegarden to do the capture and editing of the MIDI. It also supports capturing and playing back audio along with the MIDI, as well as the production of sheet music from the MIDI, but it is not what I would call a real digital audio mixing console.

Rosegarden uses JackD.

Ardour - When I want to delve into the word of digital audio (re)mixing, this is what I reach for. Multi-channel, multi-bus, supports per-channel digital effects plugins, and has a bit of a learning curve. IMHO, it compares well with Pro-Tools(tm), but I have only seen pro-tools used and found I could do the same with Ardour. One session I did with this ended with 5.2 mix down with separate L/R/C front, L/R rear, and sub channels. The original source was recorded from playback Rosegarden (I told you I used all of these for different things!) and then mixed.

Ardour uses JackD.

Pulse Audio

[Warning, this is pure opinion and rant....]Pulse audio and any serious sound work do no mix. I don't do serious sound work, but I run 3 sounds cards in my machine. I had them running very well under ALSA (yes, it took a bit of work). When Ubuntu shoved Pulse Audio down my throat, I spent several long nights trying to get things happy again and get the right sound card mapped to the right place. I then finally uninstalled Pulse Audio, and reverted to my ALSA setup and could get things going again. YMMV