Free and/or open source alternatives to paid or battery drain Android apps

Free and/or open source alternatives instead of Google apps or play (market) store apps

They have

1) less memory consuming

because these apps are
2) free, ad-free and/or opensource

nevertheless they have

3) unique features like no account required and / or offline use (of cource if possible)

Like you can use VLC instead of paid MX media player with no-ads too.

Also [non open source] offline maps that allow to download only required regions:

maps me

or you can scan all installed apps with virustotal without having permanent RAM consuming by some antivirus software:
virustotal mobile
or free (probably they closed the source code in last updates) clipboard manager that allow you to keep all copied text fragments in the app:
clip stack (4MB!)

Mostly such apps can be downloaded from free/libre app store that doesn't require an account

Under construction so now

List of top underrated android apps

temporarily placed here:

https://vk.com/page-120200044_53479414

VPN we can trust as much as possible trust to foreign administrations

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