Manit - man it every minute.

Tcl/Tk

• Tcl/Tk Documentation (8.6) | 8.5
• string - list - array - dict - file - chan - socket
• regexp - regsub - re_syntax - foreach - glob - open
• set - unset - expr - proc - namespace - oo::class
• after - fileevent - trace - vwait - coroutine - thread - tpool - exec
• apply - tailcall - refchan - transchan - info - interp
• http
• Tcllib - TclX
• SQLite Tcl Interface

Shell

• Bash
• find - locate - ls - cp - mv
• cat - tac - head - tail - more - less
• grep - sort - awk - sed
• gzip - gunzip - tar
• curl - ssh - rsync
• top - ps - free - df - du - dd - uptime

Linux

• /hier - /proc - mount - crontab
• Linux Man Page
• Linux Programmer's Manual
• Git Documentation (1.8.5)

Database

• SQLite - Small. Fast. Reliable.

Web

• CSS Snapshot 2010
• zepto.js - Lightweight jQuery-compatible API
• Vue.js - The Progressive JavaScript Framework

Program Language

• PHP Manual (7.1.0)
• Python Documentation (2.7.12)

Document

• man(1) - man(7) - mdoc - mandb - manpath
• groff