I like to use solo games to generate ideas and do some play through for setting filler.

"Five Leagues from the Borderlands" is good for overland where as "Four Against Darkness" works for dungeon crawls.

What other solo games are out there that I might have missed?

Things that can be used to generate your own background / history material for a setting.
As well as just being fun to play through on their own.

Something based around establishing or making a safe holding or town preferred.

Scarlet Heroes has a solo play option that might be good for establishing backstory.
Seems to use more detailed rules though which might slow down its use as a quick run through.

Could you explain what a solo game is in this particular regard?

In effect the GM runs everything but the charts and die rolls determine the outcomes.
This is really good for "what if" tests of story ideas and systems.
It also helps to develop an active environment, backstory for areas and characters.

Also good if you really want to "play to see what happens" and all you can find are flaky players.

The GM uses dice to make the character choices so you don't need other people to play them.