Migration to Drupal 6.1

Module

Drupal 5.1

Drupal 6.1

comments

advpoll  5.x-1.0-beta4    disabled
aggregator  core  core  
block  core  core  
blog  core  core  
blogapi  core  core  
book  core  core  
cacheexclude  5.x-1.x-dev 6.x-2.1  official release
chatroom     disabled
color  core  core disabled 
comment  core  core  
conference  5.x-1.x-dev  not available we don't use this module anymore
contact  core  core  
diff  5.x-1.1 6.x-2.1-alpha1 stable version 
drupal  core  - disabled
event  5.x-1.x-dev  6.x-2.x-dev only dev version 
eventrepeat  5.x-1.x-dev  not available  
fckeditor  5.x-2.1-beta2  6.x-1.3  official release
filter  core  core  
forms  5.x-1.x-dev  not supported
 anymore
see alternatives at
http://drupal.org/project/forms
forum  core core disabled
front (front page)  5.x-1.8  6.x-1.x-dev  dev version
help  core  core  
image  5.x-1.7  6.x-1.x-dev  first upgrade to 5.x-2.x
img_assist  5.x-1.5  6.x-1.0-beta1 official release
legacy  core  -  disabled
locale  core  core  
masquerade  5.x-1.1  6.x-2.0-alpha3  
menu  core  core  
node  core  core  
nodefilter  5.xxxx  

 I think this module is called 
"node type filter"
http://drupal.org/project/node_type_filter

official release for D6 provided

nodewords  5.x-1.2  6.x-1.0

official release
module also known as "meta tags"

og  5.x-3.1  6.x-1.3  official release
og_mandatory_group  5.x-1.0  6.x-1.0-beta1  official release
path  core  core  
pathauto  5.x-1.1  6.x-1.x-dev only dev version available
phonebook  5.x-dev    STAR module
ping  core  core  disabled
poll  core  core  
profile  core  core  
search  core  core  
sections  5.x-1.0  6.x-1.0 official release
site_map  5.x-1.x-dev  6.x-1.x-dev only dev version available
starnotes  5.x-dev   STAR module
starpresentations  5.x-dev   STAR module
starpublications  5.x-dev   STAR module 
startheses  5.x-dev   STAR module
statistics  core  core  
stcon  5.x-1.x   STAR module 
stmeet  5.x-1.x    STAR Module
subscritpions  5.x-1.9   6.x-1.x-dev beta version but comments say it's working fine
survey  5.x-1.x-dev not supported anymore  for alternatives look at
http://drupal.org/project/survey
system  core  core  
taxonomy  core  core  
throttle  core  core  disabled
tinymce  5.x-1.x-dev  not available  we don't use this module anymore
tracker  core  core  
upload  core  core  
user  core  core  
user_status  5.x-1.1  core  
views  5.x-1.6-beta5 6.x-2.5  official release
vimcolor  5.x-1.0    not maintained anymore (last version from 2006 - http://drupal.org/node/21368/release)
votingapi  5.x-1.5  6.x-2.x-dev only dev version available
watchdog  core    replaced by syslog in D6 as far as I understand

 new core modules in Drupal 6.1

dblog, openid, php, syslog,translation, trigger,update

Upgrade

(most important changes are : format of items[] in _menu() , format of links: l() and url(), the way a title of the page is set up, no arg() usage in _menu() function. Solutions to all those issues (and many more) can be found here.