Free WordPress.com alternative with better tagging

Question

I made a small website to catalogue games I've used in my ESL classes (teachingwhimsy.wordpress.com). I wanted to sort the games with custom taxonomies, a.k.a. groups of tags, but it turns out those are only available on WordPress.org, which requires you pay for hosting. WordPress.com gives you categories and tags; if you want more than those two groups, you're out of luck. (I've resorted to manually listing tags and categories in the sidebar, but it's hard to redesign if I change my mind.) Filtering by multiple tags is not possible.

I hope to be moving on from English teaching and will probably stop adding to the site in about a year, but I still want it to be useful - hence the requirement for a free package that'll stand on its own when I've stopped adding to the page.

Are there any WordPress.com alternatives that let you have groups of tags?

Essential:

• custom tag groups (e.g. "esl level tags", "group size tags", "topic tags" …)
• free, or small one-time fee
• ready-made themes, as otherwise I'll waste time faffing around with design

Optional but would make me happy:

• filter by multiple tags (e.g. show all posts tagged with "grammar" and "small group")

I don't need:

• my own domain
• a lot of space
• an ad-free website

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I've considered

• Wordpress.com (current site)

  Pros: elegant, idiot-friendly, allows tag editing
  Cons: tagging is troublesome, idiot-friendly

• Wordpress.org

  Pros: very flexible, many excellent plugins to help with tags
  Cons: need to pay for hosting

• Dreamwidth / Blogger

  Pros: tag list instead of tag clouds
  (can sort tags by prefacing with a category, e.g. "cat: grammar" or "p: 2+")
  Cons: really outdated design

• Tumblr

  Pros: plenty of themes, can customise CSS at my leisure, multiple tag search
  Cons: rudimentary tagging, search function is iffy

• Wix (still looking)

  Pros: ???
  Cons: ???