Grimbeard is a favourite of mine, he focuses on mostly niche retro games with a lean towards horror

Along the actual science line there's also Explosions & Fire, an Aussie making explosives in his garden shed. He's got a sister channel called Extractions & Ire as well where he makes other chemicals with more detail.

To be fair, neither do we

For simple apps like that I usually check out F-droid see if any open source versions exist. Might not be as feature rich but there's two GPS speedometer apps on there

Status Bar Speedometer (Display your current speed as notification) https://f-droid.org/packages/ch.rmy.android.statusbar_tacho/

Blue Square Speedometer (Simple speedometer & GPS viewer) https://f-droid.org/packages/net.nhiroki.bluesquarespeedometer/