As you may have seen over the last week and a half, many open source projects have moved off of Freenode in favor of https://libera.chat or https://www.oftc.net/, both of which offer easy replacement options to Freenode. In short Libera.Chat is composed of many folks who helped operate Freenode over the years and have their reasons for leaving Freenode while OFTC was created some time ago for Free and Open Source software projects. More reading on the subject can be viewed here and here.
An important note which prompted this sticky is that there have reports of hostile takeover of channels on Freenode: Ubuntu, Gentoo, More. If you've been a part of an IRC channel in the past, please be aware that the operators may no longer be associated with the project and the channel should be avoided if that's the case.
Some projects that have moved to Libera.Chat include the below but is no means an exhaustive list nor will it attempt to be. Please check with your projects main website or other channels if they've moved their IRC presence.
Many have opted to keep a presence on Freenode and Libera, such as Pidgin. Others have moved to https://www.oftc.net/. Many projects are still deciding on next best steps. This is very much a migration (or not) in progress.
Other projects are considering a full switch to Matrix-only as their channel already had a bridge to Freenode. As I understand it, Libera bridge to Matrix is WIP. You can join a matrix homeserver or run your own to view Matrix channels, many of which contain a bridge to their Freenode Channel and should have a smooth transition to Libera. The main Matrix instance is a bit overloaded (but always improving), so using a separate homeserver that fits your usual FOSS philosophy would be beneficial for all.
As mentioned above, the list isn't meant to be exhaustive but you're welcome to post a r/linux submission when a project migrates. Please don't submit project specific discussions about whether or not to migrate, though.
Please see the StreetComplete AMA here, and as always you can browse past AMA's here. If you're part of an open source or otherwise Linux related project, please PM the mods and we can setup a date for AMA's.