[Sony Xperia S, Acro S, Ion] letama:
Pre-requisite

Currently, if you don't want to loose your current data, you have to be on a rom that has already be repackaged. By default, bootmanager installs Sony 6.1.A.2.55 kernel, so if you're using this firmware, no need to reflash it. For all the other roms, you will have to reflash the repackaged zip in the list below after installation. Don't wipe data/factory reset and you should be good to go. In both case, backup your stuff with Titanium Backup or something else!

Note: you won't be able to restore your previous cwm backups!

Installation:

Minimal setup:

Download bootmanager_0.8.zip (mirrors) (previous version bootmanager_0.6.zip).

Download one of the modified custom firmware in the list below

Install bootmanager zip from your current recovery or extract dual.elf and flash it from fastboot.

Reboot

If your previous rom was not 6.1.A.2.55 based (like cm10 or aokp for instance), reflash your firmware from TWRP for native with one of the native firmware listed below.

Reboot

Now, if you want to use dual boot functionnality:

Select TWRP for loopback

The first time, as you don't have loopbacks files on your internal storage, it will ask for system and data partition sizes. Be patient, it could take time to create them.

When finally recovery is displayed, select erase data/factory reset

then do erase system in partitions/format system

loopbacks are now ready, you can flash one of the available build repackaged for loop.

optionally flash regular google apps from here.

Upgrade from 0.6 or higher:

Upgrade should keep your existing firmwares,

optional, but highly recommended, backup your stuff with cwm and/or Titanium backup.

start stock or custom recovery

flash bootmanager_0.8_upgrade.zip (mirrors)

reboot

re-enable dual boot in settings

Recoveries:

Starting with 0.8, offline charging has been added to twrp. As it's not possible to add to cwm, it is highly recommended to stay on twrp and avoid cwm as it's much safer for your phone.

Starting with 0.5, you can choose between cwm and twrp and switch as you wish. Just flash with your current recovery the recovery you want:

- TWRP 0.8.0 (mirrors) (previous TWRP 0.6.1)

- CWM 0.8.0 (mirrors) (previous CWM 0.6.0)

- EXPERIMENTAL, please read this before installing, TWRP 0.8.2 TWRP 2.6.0 and new 3.4 bootmanager kernel.

Firmwares

Stock / native partitions (flash them from stock recovery)

Sony 6.1.A.2.45 (don't pay attention to filename, this is 2.45, not 2.56, it's a silly typo). Note: you don't have to flash it if you have stock already, it will become useful only later on.

Sony 6.1.A.2.45 addon unsecure kernel, Sony stock kernel only, with ro.secure=0

Sony 6.1.A.2.45 addon kernel modules, Flash this is you have wifi problem, (mostly useful if your firmware was using a custom kernel).

Sony 6.1.A.2.50 stock firmware with unsecure kernel.

Sony 6.1.A.2.50 addon Standalone unsecure kernel.

Sony 6.2.B.0.211 stock firmware, rooted, with busybox.

FXP 137 CM 9.1, original firmware thread here.

AOKP ICS m6 beta 1, thanks to Apology11 for repack! original firmware thread here.

Krabappel2548's KA19, mirrors, original firmware thread here.

Sony 6.1.A.2.55, mirrors, untested unsecure kernel only here.

FXP 147 CM 10, mirrors, original firmware thread here.

PA 2.55 17/11/2012, mirrors, original firmware thread here (kernel from FXP147)

AOKP JB Milestone 1 r1, mirrors, original firmware thread here.

FXP 148 CM 10, mirrors, original firmware thread here.

PAC 18.0.0, mirrors, original firmware thread here

FXP 150 CM 10, mirrors, original firmware thread here.

PA 2.55.1 17/11/2012, mirrors, original firmware thread here

FXP 150a CM 9.1, mirrors, original firmware thread here.

FXP 151 CM 10, mirrors, original firmware thread here.

Nova Xperia RC1, mirrors, original firmware thread here.

FXP 152 CM 10, mirrors, original firmware thread here.

PAC 18.0.2, mirrors, original firmware thread here

Nova Xperia RC2, mirrors, original firmware thread here.

Hei1125's unofficial cm10 20130109, original thread firmware here.

FXP 201 CM 10, original firmware thread here.

FXP 206a CM 10, original firmware thread here.

My JB 4.2.2 aosp build, beta 2, thread is here.

My JB 4.2.2 aosp build, beta 3, thread is here.

My JB 4.3 aosp build, alpha 0, thread is here.

My JB 4.3 aosp build, alpha 1, thread is here.

Custom / loopback partitions (flash them from custom recovery)

Sony 6.1.A.2.50 (buggy, will update soon).

Sony 6.1.A.2.50, kernel only.

Sony 6.1.A.2.55, mirrors (tested, is working properly).

Sony 6.2.B.0.211, stock firmware, rooted, with busybox.

MIUI 2.9.7, mirrors, original firmware thread here.

AOKP ICS m6 alpha 2, original firmware thread here.

Krabappel2548's KA19, mirrors, original firmware thread here.

FXP 145 CM 9.1, mirrors, original firmware thread here.

FXP 147 CM 10, mirrors, original firmware thread here.

PA 2.55 17/11/2012, mirrors, original firmware thread here (kernel from FXP147).

AOKP JB Milestone 1 r1, mirrors, original firmware thread here.

Sony stock Gingerbread 6.0.A.3.75 UK, mirrors. (enabling data makes the phone reboot for me, baseband/radio problem).

Sony 6.1.A.2.55 unsecure kernel only, mirrors

XTXperience 7, mirrors, original firmware thread here. Flash 6.1.A.2.55 kernel with it.

FXP 148 CM 10, mirrors, original firmware thread here.

PAC 18.0.0, mirrors, original firmware thread here

MIUI 2.11.5, mirrors (you have to flash one of these kernels)

FXP 150 CM 10, mirrors, original firmware thread here.

PA 2.55.1 17/11/2012, mirrors, original firmware thread here

FXP 150a CM 9.1, mirrors, original firmware thread here.

Nova Xperia RC1, mirrors, original firmware thread here.

FXP 152 CM 10, mirrors, original firmware thread here.

PAC 18.0.2, mirrors, original firmware thread here

PAC 19, original thread here.

Nova Xperia RC2, mirrors, original firmware thread here.

JellyBear 3.35, original firmware thread here.

Hei1125's unofficial cm10 20130109, original thread firmware here.

FXP 201 CM 10, original firmware thread here.

XTXperience 8.1, original firmware thread here.

FXP 206a CM 10, original firmware thread here.

Ubuntu Touch 0.0.0, thread is here. Note: BIG 540 MB download. It installs on a separate 1.2 GB loopback created by the installation zip.

DooMLoRD Sony JB 6.2.B.0.197 leak, original thread here, credits goes to DooMLoRD

My JB 4.2.2 aosp build, beta 2, thread is here.

My JB 4.2.2 aosp build, beta 3, thread is here.

My JB 4.3 aosp build, alpha 0, thread is here.

My JB 4.3 aosp build, alpha 1, thread is here.

Mirrors of few builds, thanks to elpelas

Repackager package for linux 64 bits, unzip and untar, run as root: ./repackage.sh source_file out_name