Check that coin's Github, if they are active there will be frequent commits. Here is example of EOS's github
You will find project's github link on website. If there is not any, you should avoid it.
You can check the developers & community activities of a particular cryptocurrency by visiting https://www.coingecko.com/
You can directly go to this link:
Then the display page will be like this and you can see the ranking of the cryptocurrency based on their active developers and active community.
From this, you can check that Bitcoin comes first in the list and then follows Etherum, then Monero, then EOS and it follows like that. So bitcoin is at the top in terms of developer's activity too.
You can see that the developer's activity and community activity is displayed in percentages in this page and from that you can judge how active the community is and their developers.