CHESS#1273
Since it's Diwali, let's do a run through of some of the stuff on every serious player's wish-list. I'm assuming you have a reasonable computer, with a fair amount of RAM and a multi-core processor. You need a comprehensive database, engines and a program to run the engines and databases.
There are many free databases. But the Chessbase Mega Database 2017 (~4,999+ GST for 6.8 million games all the way from 1560-2017) and the Chessbase Corr Database 2018 (~5,999 for 1.4 million correspondence games) are the best. About 100,000 of these games are annotated, often by the players. Both are available for download from Chessbase India.
There is also the Convekta Chess Assistant series. Subscriptions to New in Chess or a Chessbase.com premium account wins full access to online databases at these popular sites. (Free registration allows use but not downloads.) Chessbase offers its own popular Chessbase program (Ver 14 is current - ~2,999) for access to databases. Chessbase Light is a free game-reader with fewer functions. Chess Assistant also reads the standard database formats.
You need a GUI (graphical user interface) program to read games and use engines for analysis. Arena, Tarrasch, Lucas and Kvetka are free GUI programs, and Chessbase's Fritz series comes bundled with several engines. You can buy and download sundry engines and add them to these GUIs. There are innumerable strong, free engines. Among the strongest is the free Stockfish and its android brother, Droidfish. Droidfish on a low-end smartphone would beat Magnus Carlsen.
Sometimes the latest engine versions are paid but earlier iterations are available for free. The more popular engine series include Fire, Komodo, Stockfish, Houdini, Rybka, Fritz, Junior, Shredder, et cetera. Every engine has different quirks and different opening books. So they'll come up with different styles and ideas. Some have special features like Monte Carlo analysis — the engine plays many games against itself from the same position to "understand" it. Other engines allow strength reduction to give humans an egoboosting chance.
The annual Top Chess Engine Championship is the real world championship. THE DIAGRAM, BLACK TO PLAY (White: Houdini 9601 Vs Black: Stockfish 151013, TCEC-5 2013) led to the fantastic 29. Ncd5! [Now 30.Nxb4 Nxb4 31.Kb1 d5 loses] 30.exd5 Nxd3 31.f6 [31.Qxd3 Bxf5 32.Qc3 Bxc2 33.Qxc8 Rxc8 34.Rd2 Bxb3 35. Nc3 Be7 36. Rg2 h6 37. gh6 g6 is a position even humans would win]
Play continued 31...Bf5 32.cxd3 Rxb3 33.Nc3 Rb4 34.Kb1 Rd4 35.fxg7 Be7 36.Qe3 Bd8! 37.Kc2 Ba5. Black's light squares attack can't be stopped after 38.h3 Bxh3 39.Bd2 Bf5 40.Be1 Kxg7 41.Kb1 Qa6 42.Kc2 Bb6 43.Qg3 Kg8 44.g6 hxg6 45.b3 Rg4 46.Qf3 Bd4 47.Qe2 Rg1 48.Rc1 (0-1). Since 48.Rc1 Bh3 49.Bd2 Rg2 50.Qe4 Rf2 and Bf5 is unstoppable.