Updated: Sep 14, 2021
Earlier this year, I started a Slack workspace for Delphi programmers and it has slowly grown to over 300 members, but it currently sees little activity. More activity is seen on a daily basis on a Telegram group that I setup a few months ago. The group is over 500 members and is freely available at: https://t.me/delphidevelopers This might even be the largest English speaking Telegram group available for Delphi. There are many Telegram groups out there, including multiple groups dedicated to Delphi. Here is an Indonesian Delphi group with over 1,400 members, which might be the world's largest Delphi group on Telegram: https://t.me/delphiindonesia
Update: I was just informed on Telegram that "the Brazilians rule the Delphi world" as their Telegram group has 1,700 members: https://t.me/DelphiBR
Historically, Discord was very popular with the gamer community but with recent developments such as adding thread support, it is becoming even more popular outside of the gaming world. Since Slack seems to be falling away in favor of Discord, I wanted to point out that a Delphi Programmers Discord server is available and can be freely joined at: https://discord.gg/nAtEqhMHJK
We currently have about 70 members and since I haven't really advertised it until now, it is not often used. I hope to change that with this announcement by inviting all readers to join the Discord server today! (I do prefer Discord over Slack.)
Some may ask - why another public group? It's simple - because everyone has their own preferences and the world is full of choices. I might setup other groups on other services soon. If you have a suggestion, let me know!
There are a number of discussion categories currently available with more easily added upon request:
Open Discussion Channels
Third Party Components
See you online!
Note: there is another Delphi related Discord server available using this invite link: https://discord.gg/aCuyeX8YJb They are setup as "Delphi Community" and they get a little traffic. Pick your server, or join both!
UPDATE: Ivan Souza just let me know on Discord that there is a "Bold for Delphi" group available as well. Here's an invite for that group which currently has just over 100 members: https://discord.gg/sw2u8vJU
For future suggestions and changes, you can reach me on the Telegram, Discord, and Slack groups mentioned above, or directly on Twitter or LinkedIn. Here is an invite link to the Slack workspace if you still prefer using Slack.