[RPG] How to record a session

A good omni-directional microphone is a good start, if you can't have a dedicated mic for each person. I've used a Snowball switched to its omnidirectional setting before, and it's good enough for documenting a session with good-enough sound quality that you can hear everything. (For the quality of a good postcast, a single mic won't cut it and you'll want dedicated mics, and might consider a seating arrangement that prioritises recording quality and sound separation. That's beyond my experience, but sounds like it's beyond what you need anyway.)

As for software, I've used Audacity to record and post-process play session audio, for personal documentation and sharing purposes. It's well-suited to the job as it gracefully handles the very large file sizes that you'll get when recording hours of audio. As an editor and post-processing tool it is also quite powerful, and it exports to various compressed formats for fize sizes that are more reasonable for sharing.