I guess so, but sometimes you need to build something on top of these OSS projects, say a client has a requirement of something like Google Drive for his organization, you dont have to build it from scratch, just build on top of these projects.
I recently read a post by @ben
on how someone built a forum/blogging platform on top of dev.to as it is open source. That is a great example actually.
But for individuals, its best to use the free versions of these proprietary software.
In that use-case, yes OSS projects would help save time & effort.
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