Now a days ESP8266 chip based various kind of module boards are available, here below discussed about it. Olimex, Adafruit, Sparkfun, WeMos, ESPert (ESPresso) all make various modules as well.

ESPressif ESP- WROOM Modules

ESPressif is a ESP8266 Chip Designed and Manufacture. Two Different Type of ESP WROOM Modules are ESP-WROOM-02 and ESP-WROOM-S2.

ESP WROOM-02

ESP-WROOM-02 is a low-power 32-bit MCU Wi-Fi module, based on the ESP8266 chip.
Interfaces
- Conversion : 10-bit ADC,
- Network Communication Protocol : TCP/IP network stacks,
- Wired Communication Protocols :
  - HSPI
  - UART
  - PWM
  - I2C
  - I2S
ESP-WROOM-S2 uses a 2 MB SPI flash connected to HSPI, working as the SDIO/SPI slave with the SPI speed of up to 8 Mbps.
Fully Certified
- Wi-Fi Alliance, SRRC, FCC, CE, TELEC, IC & KCC Certified
- RoHS, Halogen Free, REACH & CFSI Compliant
- HTOL, ESD-HM, MSL, μHAST, HTSL
- Output Power: +22dBm peak power in FCC certificatio
Small Form Factor : ESP8266 Module can be easily integrated into space-limited devices, due to its small size.
Size : ESP-WROOM-02 – 18mm x 20mm.
ESP-WROOM-02 PCB Design and Module Placement Guide
Data Sheet : ESP-WROOM-02

ESP WROOM-S2

Size : ESP-WROOM-S2 – 16 mm x 23 mm.
ESP-WROOM-S2 Hardware Evaluation Platform
ESP-WROOM-S2

Ai-Thinker’s ESP8266 Modules

The AI-Thinker modules are succinctly labeled ESP-01 through ESP-13. NodeMCU boards extend upon the AI-Thinker modules.

ESP-01

PCB Antenna, through matching, distance do open 400 Meters, easy to use
ESP-01 Does not Support PWM hardware, But You can use the software PWM in NodeMCU Platform.

ESP-02

SMD package for the commit limit, the antenna can be used IPX End leading housing.

ESP-03

SMD package, built-in ceramic antenna technology, all available IO Leads.

ESP-04

SMD package, customers can custom antenna types, flexible design, all available IO Leads.

ESP-05

SMD package, and only leads to serial RST Feet, small size, external antenna.

ESP-06

Bottom mount technology, all IO Mouth leads, with metal shielding shell, can be had FCC CE Certification is recommended.

ESP-07

Half-hole chip technology, all IO Leads, with metal shielding shell, can be had FCCCE Certification, external IPX Antenna, built-in ceramic antenna can also be used.

ESP-07S

Same ESP-07 with 4MB Flash
Dimensions
- Size 16mm*17mm*3mm
- Pads:1mmx1.2mm
- Pads Spacing: 2mm

ESP-08

with ESP-07 Except that the antenna customers can define their own form.

ESP-09

Ultra-small size package, only 10 * 10 Mm, four-layer board technology ! 1M byte.

ESP-10

ESP-11

Chip interfaces, ceramic antenna, small volume.

ESP-12

Semi-hole patch process , all IO Leads, with metal shielding shell, passed FCCCE Certification, built PCB On board antenna, 4M byte Flash.

ESP-12E

On the basis of the ESP-12 leads to 6 feet and more, greatly enhanced anti-jamming capability, the main recommendation of this section!

ESP-12F

ESP-12S

ESP-12S Datasheet
Size : 24mm*16mm*3mm, Weight : 0.01kg.
16pins count with based On ESP8266 WiFi IC
Fully compatible with forecast version ESP-12E or ESP12F
FCC and CE & RHOS all passed
Further improved antennas design, better signal performance
Note : ESP-12S does not have a SPI pins at the bottom of the board

ESP-13

The 4-layer design, semi-hole chip technology, all IO leads, with metal shielding shell, the antenna redesigned, RF performance!

ESP-14

img class=”alignnone wp-image-335″ src=”https://www.aruneworld.com/wp-content/uploads/2017/06/ArunEworld_ESPressif_ESP8266_ESP-14_Top_BlackBorad.jpg” alt=”” width=”128″ height=”186″ />

In ESP-12E prototype design, interior adds STM8S003F3P6, and by STM8S ESP8266 AT commands to control the module is a complete STM8S micro-controller can operate via WIFI STM8 micro-controller programming.

ESP-16

ESP-16 support WiFi and GPRS

Summary of All AI-Tinkers ESP8266 Module Boards

Comparison 1 :

Variant	Dimensions	Antenna	Flash Memory	GPIO	Metal Shield Claim

ESP-01 Blue	14.3mm*24.8mm	PCB Antenna	0.5MB (500kb)	GPIO0/2/16	None
ESP-01 Black	14.3mm*24.8mm	PCB Antenna	1MB
ESP-02	14.2mm*14.7mm	U-FL Connector		GPIO0/2/15	None
ESP-03	17.4mm*12.2mm	Ceramic Antenna		GPIO0/2/12/13/14/15/16
ESP-04	14.7mm*12.1mm			GPIO0/2/12/13/14/15/16
ESP-05	14.2mm*14.7mm	U-FL Connector
ESP-06	14.2mm*14.7mm			GPIO0/2/12/13/14/15/16	Metal Shield Claims FCC
ESP-07	22mm*16mm	Ceramic Antenna & U-FL Connector		GPIO0/2/4/5/12/13/14/15/16	Metal Shield Claims FCC
ESP-07S
ESP-08	17mm*16mm	None		GPIO0/2/12/13/14/15/16	Metal Shield Claims FCC
ESP-09	10mm*10mm	None	1MB Flash Memory	GPIO0/2/12/13/14/15
ESP-10	14.2mm*10mm	None
ESP-11	14.2mm*10mm	Ceramic Antenna		GPIO0/1	Metal Shield Claims FCC
ESP-12	24mm*16mm	PCB Antenna		ADC + GPIO0/2/4/5/12/13/14/15/16
ESP-12E
ESP-12F
ESP-12S
ESP-13
ESP-14
ESP-16
DWA8	17mm*27.1mm	PCB Antenna		ADC + GPIO0/2/12/13/14/15/16

Comparison 2

Difference Between ESP-01 Blue Board and ESP-01S Black Board

Memory Flash Size
- ESP-01 Blue Board – 500Kb
- ESP-01S Black Board – 1Mb

Difference Between ESP-07 and ESP-07S?

PCB Layers
- ESP-07S – 4 Layers of PCB
- ESP-07 – 2 Layer of PCB
Flash Memory
- ESP-07S – 4M
- ESP-07 – 1M
IPEX Connector and Ceramic Antenna
- ESP-07S – Only have IPEX Connector and not have ceramic antenna
- ESP-07 – Have IPEX Connector and ceramic antenna
Certification
- ESP-07S -Have FCC, CE, ROSH Certification
- ESP-07 – 1M – Not have certification
Note :
- ESP-07S is upgraded from ESP-07.
- Both are same pins

Difference Between ESP-12E and ESP12F ?

Bit difficult to identify the ESP-12E and ESP12F. Because not mention in the shield. But Some modules Prints in back side. if not printed back side of the module, you can easily identify by antenna design. please refer the antenna design in the above ESP-12E and ESP-12F images.
PCB Layers
- ESP-12F – 4 Layers of PCB
- ESP-12E – 2 Layer of PCB
Certification
- ESP-12F -Have FCC, CE, ROSH Certification
- ESP-12E – 1M – Not have certification
Note
- ESP-12F is upgraded from ESP-12E.
- Both are same pins

See more reference websites

aithinker blogspot

Bolt IoT (Pune-2016 Iot Award)

See More : Bolt IoT (Pune-2016 Iot Award)
- Ai-thinkers ESP Module + SD Card + Atmel328P IC

Olimex ESP8266 Module

Olimex MOD-WIFI-ESP8266
Olimex MOD-WIFI-ESP8266-DEV

NodeMCU DEVKIT

ESP8266 NodeMCU Dev has an Ai- thinkers ESP8266 module on it
It comes with the latest version of AT Firmware already setup on it, together with all the drivers we are going to use
Note: The D0, D1, D2, … numbers printed on the board are different from what ESP8266 Module uses – because originally those boards were made for a different pins determine.
Make sure to refer to the image above to determine which pins are which On top it has a micro-USB socket, for connecting to the computer.
Next to it are two buttons, one for reset and one for flashing.
Then on both sides of the board are two rows of pins, to which we will be connecting cables.

The symbols meaning is as follows:

3v3- this is a fancy way to write 3.3V, which is the voltage that the board runs on internally. You can think about this pin like the plus side of a battery. There are several pins like this, they are all connected inside.
gnd- this is the ground. Think about it like the minus side of the battery. They are also all connected.
gpioXX- “gpio” stands for “general purpose input output”. Those are the pins we will be using for sending and receiving signals to and from various devices that we will connect to them. They can act as output – pretty
much like a switch that you can connect to plus or to minus with your program. Or they can act as input, telling

your program whether they are connected to plus or minus.
a0- this is the analog pin. It can measure the voltage that is applied to it, but it can only handle up to 1V.
vin- this pin is connected with the 5V from your computer. You can also use it to power your board with a

battery when it’s not connected to the computer. The voltage applied here will be internally converted to the 3.3V that the board needs.
rst- this is a reset button (and a corresponding pin, to which you can connect external button).
flash- hold down this button while resetting to bring the board into programming mode (also known as flashing mode).