What is the most lightweight proof-of-work algorithm? I know litecoin was created back in the day using Scrypt as to make it more lightweight but also harder to build ASIC hardware from - so everyday computers could mine. Are there other algorithms one should be aware of nowadays? Possibly ones that require little resources and make it impractical to build ASICs.
Contrary to the name the proof of work used in Litecoin is significantly more difficult than SHA256 to verify (it slows sync times noticeably), while simultaneously not achieving it's goals of being only able to be mined on a CPU, or a GPU depending when you read the pitch on their website. It offers very little resistance to being mined on a GPU or ASIC, in fact its design is extremely well tailored to linear time-memory tradeoffs, which make the hardware cost even cheaper. Being harder to make an ASIC for isn't an asset either, it just means that they become less commodity hardware and more likely a monopoly of one or two players. 

SHA256 is about as lightweight and as simple as you can get, avoiding hardware acceleration is not an achievable goal and probably not even desirable even if it were.