A handy text editor should have these functions built in or have plugins making up the missing piece.

Functions SublimeText Plugins VS Code Extensions
Ascii Art ASCII Decorator MDTools
Diff Diffy Partial Diff
Evaluator Eval eval
Format All kinds of formatters All kinds of formatters
Git SublimeGit Built-in
Issue tracker GitHubIssue GitHub Issues
Markdown Highlight Markdown Light Built-in
Markdown Preview Markdown Preview Preview
Pomodoro Pomodoro TodoPomo
Project manager Built-in Built-in
REPL SublimeREPL JS Eval Replace / Clojure Code / …
Search/Index Search in Project Built-in
Snippet All kinds of snippets All kinds of snippets
Spell check KeyboardSpellCheck SpellChecker
Static file server SublimeServer StaticServer
Symbol Tree Built-in Symbols Treeview
Table maker Table Editor Table Formatter
Task/orgmod Plain Task To Do Task
TODO TodoReview Todo Highlight