Great post @Alpha18. I share similar views to the other comments - useful but noting the limitations of some of the sites we might try and use as investors.
I'm a BIG fan of culture and any clues I can get that might provide insight into what's going on under the hood. Anything that might help me get a leg up re: better understanding the company I will typically try and explore. I am no expert by any means - but think the culture side of things is often put to the side as trivial or not so relevant, when in fact it should be a top 2 or 3 consideration, particularly with microcaps.
I use Glassdoor but I don't normally take too much notice of it. I do however look for lots of five star reviews in a short time frame (a sign the business might be trying to enhance its reputation by asking staff to leave positive reviews). Nuix is the one that comes to mind, it was clear they were doing this when they were pushing shit up hill last year. It also helped that they were outed by a specific individual who indicated they were doing just that, but the signs were clear. In addition, a few isolated one star reviews are normally a good way for an annoyed ex staff member to feel better after their employment didn't work out, so I don't normally take too much notice of these either. That said, anything that might provide insights and I am all ears.
I find Seek, LinkedIn etc can be valuable for tracking staff hiring - both as a vetting mechanism but also keeping in the loop with companies I hold. Given the familiarity we might have with our holdings, I think we should gain some valuable clues re: trends or any patterns in recruitment. It might reveal expansion underway but also might reveal issues at particular sites - eg staff turnover due to asshole manager. Regular job advertisements and/or issues filling a position might also be an indicator of poor culture, company reputation or more broader issues with skill shortages.
The best example for me at the moment is two of my larger holdings (ABB and PLY) are both expanding to new states across Australia. I am keeping tabs on job advertisements and how long these remain up for any clues I can glean.