Right now the world is doing a "little" remote work experiment. The first troubles already come when the right tool needs to be chosen.
Free Conference Call
As the name suggests, this tool is free. It allows chats, conference calls, and online meetings with screen sharing.
Microsoft Teams
In the basis version Microsoft Teams is free. The full version comes with any Office 365 subscription, which should be available in most (larger) companies. It supports chats, real-time collaboration, video conferences, and is extensible. The tight integration with Office 365 makes it very appealing.
Meet Jitsi
An open source video conferencing tool. The website allows creating frictionless web conferences without any registration. The sharing capabilities are sufficient for quick purposes or for an integration in existing products.
Zoom
Zoom is a quite established product on the market. The basic subscription closes a meeting after 40 minutes. A pro version costs about 15 € per month. Its unique feature is a "raise hand" gesture, which allows moderation with ease.
BlueJeans
A video conferencing tool for up to 30 participants. A quite simple and rudimentary service, but very reliable. The app comes with a whiteboard functionality. Only the first 2 weeks are for free, afterwards a subscription is available on a monthly basis (19 € per month).
DFNconf
This is based on Pexip and hosted by the DFN. Fully hosted in Germany and for free for people connected to the DFN (e.g., most universities).
Google G Suite
Google's G Suite has quite some offerings for communication. Most importantly, Hangouts / Meets can be used to alleviate the real-time communication need. A special free version for educational purposes is available.
Skype for Business
Skype for Business (formerly Lync) is mostly replaced by Microsoft Teams, but still exists as an independent tool. It is bound to the Office Communication Server and costs a license fee. It can, however, work on premise and without any third-party dependencies.
Adobe Connect
There are three versions of this tool: One for meetings, one for webinars, and a third one dedicated to lectures. However, this tool requires a paid subscription after the trial period of 90 days expired. The virtual class room offers video conferences, moderations, file sharing, and whiteboarding capabilities.
Cisco WebEx
A simple video conferencing tool. Participants can draw on a whiteboard or on prepared slides.
Vitero
Vitero also allows separate working groups in different "rooms". Another unique feature are post its. This way important notes are always present and will not be forgotten.