Callpage - Turn website visitors into sales calls. Use CallPage and provide immediate free phone callback to your leads in 28 seconds.
data.world - The social network for data people
Upcall - Upcall enables you to crowdsource your outbound calls. Collaborate with 1000+ on-demand callers worldwide for sales, marketing and customer support calls. Free trial.
Datawhale - Powerful people data for enterprises.
HeyHi.sg - Video call with interactive whiteboard
DataQuest Beta - Codecademy for Data Science