TalkChess.com

Hi,

I know about some online tactics training puzzles like these:

https://lichess.org/training

https://tactics.chessbase.com/en/

https://chesstempo.com/chess-tactics.html

One question I have for now, is that can we have an offline version ?

You can find chess puzzles here :
http://wtharvey.com/
Srcoll down for pgn.

An interesting book from Laszlo Polgar : "Chess: 5334 Problems, Combinations and Games" (also in pgn).

https://github.com/pychess/pychess has offline tactics from several sources.