Never Solo'd. What activities do you love? What story artifacts do you make?

Never Solo'd before. Sad, I know. I still admire the practice and plan to test the play style soon.

My friend and I are building something. We think Solo Roleplaying needs some tool love. There is a world where your writings and your spoken words become a living world. You make the lore, our tool does the organizing.

We don't yet have note taking, and our communication tools are most useful for groups not solo play. However we're looking for what to build next and we think supporting this community would be great.

I'm curious about all you long time Solo'ers, what kinds of story artifacts do you create? Just notes/docs? In game letters mailed to other characters? What else?

Please help this total noob here understand the breath of interactions and activities this play style has to offer.