Direct answer
If you only want to play, freeware is enough. If you want to modify or redistribute, stay with a page that shows an open-source, Creative Commons, or public-domain license file.
Read the license on the game page, not this summary. This page explains the labels. The file, when we have it, is the evidence.
Do not fork, sell, or ship a mod of a freeware game just because this site hosted the download.
Play a freeware title if you only want to play. Modify or share a game only when its page includes an open-source, Creative Commons, or public-domain file. This summary is not that file.
Games with source code available under open source licenses
Games licensed under Creative Commons, allowing sharing and modification
Free to download and play. That is not permission to fork, sell, or ship a mod. If the game page has no license file, stop at playing.
Games in the public domain, free for anyone to use