“SEC filings for humans.” The site was created in 2014 by Maris Jensen, a former SEC employee with the mind of an analyst and the soul of an artist. It offers a simple and elegant view into the documents filed with the SEC by public companies, searchable by filer (person or company). It’s strength is in showing connections between companies and people using beautiful graphics, but it also shows the nitty gritty financial details in charts and tables if you prefer. What it doesn’t do is summarize compensation and holdings for insiders.
Though it is based on documents filed with the SEC and, thus, all about public companies, you can also learn about Form D fundraising by private companies.