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emu-ex-plus-alpha
Multi-platform computer & game console emulation system including supporting code (EmuFramework) and core engine (Imagine)
As to specific emulators for the older stuff I recommend the .EMU emulators from Robert Broglia. You can get them all for free on his GitHub page https://github.com/Rakashazi/emu-ex-plus-alpha/actions/runs/4780747948 but you will need a GitHub account to download them. If you end up liking them then you can buy one or more to support the developer.
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SaaSHub
SaaSHub - Software Alternatives and Reviews. SaaSHub helps you find the best software and product alternatives
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Drastic https://play.google.com/store/apps/details?id=com.dsemu.drastic is the best choice for DS emulation. It's paid but it genuinely is worth the money. There is also MelonDS https://github.com/rafaelvcaetano/melonDS-android but it's not quite as good but can play DSi games where Drastic cannot.
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For 3DS go for Citra https://citra-emu.org/download/. On that link click on Manual Download and then grab the latest Nightly build. There is a fork called Citra MMJ that can give better performance on some hardware and that can be found here https://github.com/weihuoya/citra/.