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