This quick guide should somewhat help you no matter if you want to keep your old stuff because you're not fond of e-waste (or broke), or want to switch because modern tech makes you more distracted and paranoid than productive. I wrote it in 2024, but I'll try to keep it updated!

1. Computer/laptop

What to consider:
-multi-core non-energy saving CPU. Treat userbenchmark.com as more reliable than mere specs like the clock rate,
-try adding RAM - nowadays DDR3 is really cheap and might be easier to get than an already maxed-out laptop,
-switching from a magnetic HDD to any SSD really does improve the performance a lot,
-if you want to try playing games, try to get the latest AMD GPU you can afford (nowadays they're generally cheaper than comparable nVidias),
-look into undervolting or at least lower the maximum processor state in power options if you want to keep it working for a long time,
-use a lightweight operating system, browser, and ad-blocking software (recommendations below),
-keep it clean so it doesn't overheat,
-don't be afraid of big-ish (i.e. totaling at 12GB together with physical RAM) swap files, especially with an SSD,
-if you're unsure if your computer is slow because of some software issue/data bloat or not, try booting up some live lightweight Linux distro (Lubuntu maybe?) and see if it runs (not boots!) much faster - if so, it could be the bloat indeed and you might benefit from reformatting the system drive.
TL;DR: SSD, RAM, lightweight OS & browser, non-low power CPU.

(Subjective) recommendations:
-really do avoid the low power CPUs (Intel Atom, etc.) - for example, a Core2 Duo T9400 from 2008 is 1/3 faster than an A6-9200 released almost 10 years later according to benchmarks!
-no matter which browser and Windows, I recommend uBlock Origin and TinyWall,
-also to avoid: no-name brands, and models that are known to cause issues, obviously (search for reviews and ratings online),
-some of my favorites are: IBM/Lenovo ThinkPad (esp. T450), Dell Precision (esp. M4800), HP Zbook - and none of the soldered RAM + low power CPU ones,
-ultra low spec (<=2GB/1 core) OS + browser recommendation: AntiX + Dillo (or Windows XP 2019 + Basilisk if you're more insane than me) - definitely still able to run programs like (offline) media players, some light musicmaking software (OpenMPT, Renoise, Reason), office stuff, old games, 8-16(-32?)-bit era emulators, etc,
-~3GB, ~1.5GHz 2 core: Lubuntu/old Mint LTS + Falkon (or Windows 7 + Waterfox if you have a very good firewall and a lot of faith, or no internet) - this tier should be enough to browse modern internet and watch some streaming video,
->=4GB, closer to 2GHz 2 core: newest Mint + Falkon (or debloated Windows 10 LTSC + Waterfox) - I use something like this as my daily driver, and it runs multiple browsers, full HD video, Ableton Live 11 and Lightroom CS6 just fine!

2a. Modern app-capable phones

What to consider:
-paying more for more RAM in hopes of making your purchase more future-proof seems to work - I still use my 6GB phone from 2016 just fine,
-you need to either get something with good manufacturer support so new versions of Android will officially keep coming out, or with strong off-market community so you can update it by yourself,
-contrary to the popular belief, rooting and/or switching to alternative firmware still does make a difference in terms of battery life and more (mostly because of the firewall, CPU clock control and debloat),
-disabling built-in non-removable apps doesn't affect the storage, but it can affect the performance and/or battery life if said app would otherwise run in the background,
-order at least two screen protectors even before you get the phone.

(Subjective) recommendations:
-DooGee S96 Pro (cheapest rugged device with modern specs), Motorola G23 (cheapest 8GB device), OnePlus 3T (oldest - and thus probably cheapest and smallest - device that still runs modern apps as of 2024),
-Via (fastest and adblock-enabled browser), Aurora/APKPure (anonymous Google Play tunnels) or F-Droid (non-Google open source-focused alternative) as Google Play replacements, NextDNS (free system-wide adblocking DNS server), Hacker's Keyboard or OpenBoard (more privacy-focused than the mainstream ones), OsmAnd (non-Google maps & navigation), MuPDF mini (ultra lightweight ebook reader), OpenCamera (most advanced - and free! - camera app I've ever seen), Aves Gallery and Total Commander (free gallery and file manager apps),
-my favorite firmware replacement is probably LineageOS,
-even though very old Android devices might seem useless as all-in-one daily drivers nowadays, remember that stuff like PlayStation emulators, table clock apps or media center software suites exist even for Android 2.x from 2010! And some older versions of internet-enabled apps still work on Android KitKat-Lollipop (2013-2015) which may run fine on devices from around 2012 (Xperia S, Galaxy S III).

2b. Non-modern app-capable phones

What to consider:
-battery life of the individual phone,
-music, map and camera capabilities (a lot of feature phones are perfectly fine for this) - and also expandable storage if you care about these,
-supported network modes - some countries turned their 2G and/or 3G comms off in the past few years. You need just GSM for voice calls and text messages though,
-availability of accessories such as chargers and batteries.

(Subjective) recommendations:
-most featureful non-color phone with longest lasting battery: Nokia 6310i (6210 has less features but tends to be cheaper and has equally good battery, and 6510 has the same features as 6310i and is VERY light and small but the battery isn't as good),
-longest-lasting color phone: Nokia C3-00,
-most useful phones that still aren't modern smartphones: Nokia N95, Nokia E7, Nokia E72, Sony Ericsson Xperia X1, Nokia 2780 Flip,
-most durable (as in actually dust-proof etc) phones: Nokia 5210/5140/800, Cat B35,
-bonus: oldest phone that can emulate GameBoy at full speed: Nokia 6600.

3. Bonus

Most of the time, game consoles from two generations back seem to be the cheapest, and custom firmware/homebrew can definitely give them a new life. My favorites for emulation are definitely Wii and PSP. Also, the 7th generation was definitely still pre-always-online era.
Go here to read more about photographing on a budget!

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