Hi there,
below is a list of tools which is use and find usefull. Please tell me if I should add your tools in this list too.
E-Mail server
| Name | Free / Paid | Description | Link |
| DKIM Validator | Free | Validates SPF and DKIM entry of your mail. Just send an E-Mail to the given temporary address. | http://dkimvalidator.com/ |
| Mailt-Tester | Free / Paid | Checks SPF, DKIM, Spam, ... almost everything. Limited daily usage without paid subscription | https://www.mail-tester.com/ |
| Spamscorechecker | Free / Paid | Analyze the spam score of your mail | https://spamscorechecker.com/ |
| Eicar | Free | Send Eicar test viruses to your mail address | http://www.aleph-tec.com/eicar/ |
| SSL-Tools Cert | Free | Check your mail server smtp cert | https://de.ssl-tools.net/mailservers |
| SSL-Tools SSL | Free | Check if your mail transfer prevers ssl connection | https://de.ssl-tools.net/mails |
| Mail security grader | Free | Analyze your mail server (SMTP, POP, IMAP) | http://emailsecuritygrader.com/ |
| MxToolbox | Free / Paid | Mailserver Toolbox | http://mxtoolbox.com/ |
| SPF Record | Free | Checks and creates SPF records for your mail addresses | http://www.spf-record.de/ |
| Port25 | Free | Replies with an detailed report: SPF, DomainKeys, DKIM and SpamAssassin | https://www.port25.com/authentication-checker/ |
| MailRadar OpenRelay | Free | Tries different relay method agains your server | http://www.mailradar.com/openrelay/ |
| AppMailDev | Free | Tests for DKIM, SPF and DomainKeys | http://www.appmaildev.com/ |
| CheckTLD | Free | Reply with all steps a mail server is doing on receiving mails. Also checks ssl certificate. | https://www.checktls.com/perl/TestSender.pl |
E-Mail tools
| Name | Free / Paid | Description | Link |
| DavMail | Free | POP/IMAP/SMTP/Caldav/Carddav/LDAP Exchange Gateway | http://davmail.sourceforge.net |
| E-MailRelay | Free | E-MailRelay is a simple SMTP proxy and store-and-forward message transfer agent (MTA) | http://emailrelay.sourceforge.net/ |
DNSBL
| Name | Free / Paid | Description | Link |
| Blacklistalert | Free | Multi blacklist tester | http://blacklistalert.org/ |
| MxToolbox | Free / Paid | Mailserver Toolbox | http://mxtoolbox.com/ |
Gameservers
| Name | Free / Paid | Description | Link |
| GameServerManagers | Free | Wrapper for a lot of game servers for easy install, update, start/stop and monitor | https://gameservermanagers.com/ |
Generell
| Name | Free / Paid | Description | Link |
| Digicert Util | Free | Test almost every port for ssl certificates | https://www.digicert.com/util/ |