ruby is really good for solving small problems quickly. Don't get me wrong, proficiency in your shell will go a long way. But when something starts to get complicated I can bang it out in ruby and it's just done.
Web apps do drive ruby's adoption, though. Now that I know ruby I use it for many things, but I learned it initially for rails. Many other languages (like python) can fulfill ruby's scripting usages (I would argue javascript can't - despite its many strengths it's just a little too awkward)
Matches my use case completely. I haven't built a rails app but learned ruby with a view of doing that but never did (I believe it's important to know the language before the framework - in hindsight, a good decision with Rails specifically).
I like the standard library and I love the gems that fill the gaps the stdlib shouldn't really fill.
Many devs I know reach for the language they use day to day and their scripts and productivity suffer. Ruby is almost like an openly secret weapon in that sense.
Web apps do drive ruby's adoption, though. Now that I know ruby I use it for many things, but I learned it initially for rails. Many other languages (like python) can fulfill ruby's scripting usages (I would argue javascript can't - despite its many strengths it's just a little too awkward)