OptinMonster - OptinMonster helps to convert abandoning website visitors into subscribers and customers.
Mendeley - Easily organize your papers, read & annotate your PDFs, collaborate in private or open groups, and securely access your research from everywhere.
Freebiebucket - Curated free tools & resources for makers 🛠
Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.
GetSiteControl - Website popup builder & email marketing suite for ecommerce
Qiqqa - Qiqqa is a free research and reference management software. It can be used in many organizational projects from the academic to the personal to the business endeavor. Read more about Qiqqa.