My suggestions: Implement basic widget toolkit, making something that essentially works is simple (regardless whether you implement in on top of dumb framebuff

My suggestions: Implement basic widget toolkit, making something that essentially works is simple (regardless whether you implement in on top of dumb framebuffer, existing display server like X11/WinAPI or even on top of HTML). But there are lots of nuanced details that you will probably learn along the way, some of them overlap the text editor problem, then there are things like not opening windows/popup menus outside the display area (there are widely used toolkits that get this wrong even for the simplest “select box on bottom of the screen” case), clipping, handling scrolling (both detecting if something is too large and should be scrollable and actually implementing scrolling efficiently) and last but not least designing the API to be both powerful and simple to use. Simple transactional database that really has ACID semantics. Locking, BTrees, journaling, isolation levels, how to actually store all that in files. Toy unix block filesystem (there can be some overlap with previous point and for journaling design it might be better to start with the FS case). Recommended reading: https://news.ycombinator.com/item?id=12309686 https://news.ycombinator.com/item?id=12309686 And, which is maybe somehow motivated by doing this mostly pointless thing as long abandoned pet project, and thus maybe slightly nonsencial: implement AFS-like “distributed” filesystem. The interesting part there lies in RPC and authentication mechanisms, not in doing some kind of distributed consensus (thats why “AFS-like”, as AFS has single master server for each volume) And at last, although the theme is somewhat different: Implement a tool that given a path to unix file prints a list of users who have access to the file and what kind of access they have. This sounds like simple tool, but is surprisingly non-trivial even without takong ACLs into account. (This is not from me, but I read this in some similar list ~15 years ago, IIRC by Andrew Tridgell)