Keep Grinding

Good Programs for Unix-like Systems

galculator is an advanced calculator.
Git tracks changes in documents.
LibreOffice is a productivity suite that can not only replace Microsoft Office and Apple's iCloud, but also read files from both of them! If your system is weak, try Pandoc and sc-im instead.
LXTerminal is a terminal emulator.
NeoVim is an advanced text editor.
Zathura displays documents.

BleachBit is an easy way to free space on the internal storage.
Exiftool displays and alters metadata.
p7zip compresses and encrypts directories.
Redshift reduces a display's blue light. If you use xrandr to change the brightness, run that before Redshift.
rsync is a simple backup tool.

Firejail sandboxes a program to weaken any vulnerabilities. If you dislike editing configuration files, Firetools is a graphical configuration tool for it. If a program does not co-operate with Firejail, then try restricting it with AppArmor instead.
OpenVPN reroutes your connection to discourage trackers on your LAN.
signify is an easier alternative to GNU Privacy Guard.
slock, well, locks the desktop until you enter your password.
Tor is a psudonymizing proxy and an alternate internet. Just don't use it for BitTorrent.
VeraCrypt creates near-bulletproof digital safes. It doesn't seem to work properly on OpenBSD, though.

Claws Mail is one of the most secure e-mail clients out there. It even deflected the EFAIL attacks.
I2P is an alternate internet.
Lynx is a text-only browser for HTTPS and Gopher.
Newsraft reads RSS feeds.
Pale Moon is an improved version of pre-Quantum Firefox.
qBittorrent is the perfect BitTorrent client for desktops. On servers, use Transmission for better performance.
qutebrowser is a lightweight graphical web browser.
Ungoogled Chromium is an improved version of Google's Chromium, the basis of Google Chrome.

Read the linkroll for recommended extensions.

Dolphin emulates the GameCube and the Wii. If a game lags, try it in Ishiiruka-Dolphin instead.
DOSBox-X emulates Microsoft's DOS.
DuckStation emulates the PSone.
FinalBurn Neo is an arcade game emulator that has better performance than MAME.
Flycast emulates the Dreamcast.
FS-UAE emulates Commodore's Amiga line.
MAME emulates arcade games, plug-and-play consoles, and oddball systems.
melonDS emulates the Nintendo DSi. Don't forget your touch-compatible monitor or external tablet!
mGBA emulates the Game Boy Advance.
openMSX emulates the MSX line.
ParaJVE emulates the Vectrex.
Phoenix emulates the 3DO and the Jaguar.
pokemini emulates the Pokémon Mini.
PPSSPP emulates the PlayStation Portable.
QEMU emulates other computers. If the command line intimidates you, VirtualBox is a graphical program that has the same purpose.
RetroArch organizes excellent emulators of the following machines: 32X, Amiga CD32, Atari Lynx, Atomiswave, Game Gear, Master System, Naomi, Neo Geo Pocket Color, NES, PC Engine Duo/Turbo Duo, PC-FX, Saturn, SG-1000, Super NES/Super Famicom, Twin Famicom, Virtual Boy, WonderMega, and WonderSwan Color.
RPCS3 emulates the PlayStation 3.
SameBoy emulates the Game Boy Color and the Super Game Boy 2.
simple64 emulates the Nintendo 64.
Stella emulates the Atari VCS/2600.
Tsugaru emulates the FM Towns.
VICE emulates the VIC-20 and the Commodore 64.
Wine is a compatibility layer for Windows programs.

OpenBSD is definitely recommended if your computer supports it. It lacks the security and design problems of other systems.
Many Raspberry Pi-oriented distros significantly fail, though DietPi fails much less.
Batocera is an excellent entertainment center. Be careful when installing it, because it will try to take up an entire disk.
If everything else doesn't work for you, try Alpine.