Online Platforms with API

ProjectHoneypot

You can ask if an IP is related to suspicious/malicious activities. Completely free.

BotScout

Check if the IP address is related to a bot that register accounts. It can also check usernames and emails. Initially free.

Hunter

Find and verify emails.
Some free API requests free, for more you need to pay.
Commercial?

AlientVault

Find Malicious activities related to IPs and Domains. Free.

Find related personal data to a email profiles on other platforms, domain basic company info ,mails and people working and companies get company info from mail.
You need to pay to access all the possibilities.
Commercial?

BuiltWith

Technologies used by webs. Expensive...
Commercial?

Fraudguard

Check if a host domain or IP is related with suspicious/malicious activities. Have some free API access.
Commercial?

FortiGuard

Check if a host domain or IP is related with suspicious/malicious activities. Have some free API access.

SpamCop

Indicates if host is related to spam activity. Have some free API access.

mywot

Based on opinions and other metrics get if a domain is related with suspicious/malicious information.

ipinfo

Obtains basic info from an IP address. You can test up to 100K/month.

securitytrails

This platform give information about domains and IP addresses like domains inside an IP or inside a domain server, domains owned by an email find related domains, IP history of domains find the host behind CloudFlare, all domains using a nameserver....
You have some free access.