Cocalc
A toolkit for coding and writing online. The UI is a bit outdated but the services are real hardcore.
Azure Notebooks
Azure notebooks is simply a hosted Jupyter notebook.
Next Journal
NextJournal is the notebook for reproducible research. NextJournal provides poly-language notebooks and beautiful UI.
Google Colab
Google Colab is an online version of Jupyter Notebook which allows us to use free computation powers from Google and storage on Google …
Agenda
Evernote
Not so lightweight but still very good for managing life especially since it has got a lot of integrations from a lot of other services.
Google Keep
Google Keep is light-weight. It comes with powerful search. The App ships with simple drawing and handwriting.