Honourable mention of Léon - The URL Cleaner, which targets the same use-case.Yet URLCheck seems more advanced on first glance.

Thanks for the recommendation!

I can recommend you ICSx5 for ical subscription and DAVx5 for calendar synchronisation.

Yet I would agree, that a good calendar app should ship with these features.

The German technology blog Kuketz has a comprehensive overview and comparison of all major messenger services.