We have at least two powerful and free event calendar plugins for wordpress, and we have tried both on live websites. Both distributed as opensource plugins from wordpress plugin repository, their contributor company rely on advanced features to make money via premium version of the plugin. All-in-One Event Calendar (AIOEC) is developed and maintened by Vancouver based http://time.ly/, has more than 100 000 downloads and is actively maintened, which is a sign of future reliability and compatibility with coming wordpress updates. Same story for The Events Calendar (TEC): it's given to you by a company called TRIBE, shows more than 300 000 downloads, and last update is just a few days ago. The team page from Tribe company is quite impressive with highly specialized engineering profiles, and the pro version is clearly distributed as a well packaged product Event Calendar Pro version, at various prices depending on the licensing, starting at 89$ / site / year.. AIOEC has its own premium version in the form of various addons.
Events basic : time place and location
AIOEC and TEC both comme with special custom fields within the editor : quite similar in their approach, they have small differences that can help you make a choice.
Typing events can be a time consuming affair : both plugins have their own custom post type within a specific wordpress admin menu. If you have many events TEC has a big advantage because it stores organiser and location information in separate tables, which helps grouping events by location and by organiser.
On the other side, if you want to go free, AIOEC allows Recurring events, while on the case of TEC this is only for the premium users.
LAYOUT AND EVENT DISPLAY
TEC also provides very nice free category color plugin, which can help you further organize events : this is a very strong argument in favor of TEC in terms of visual display on the front end. On the other side, AIOEC has a very nice card layout free extension that also allows list view, this is really nice for quick display of neat calendars. Just like AIOEC, default TEC templates need to be trimmed of extra elements you might not want to show : the default event calendar month view has a lot of extra stuff you don't need, like search engine . Detailed event view also needs trimming, depending on what kind of event you need to show.
Other significant calendar solutions for wordpress