Here is the full list of all 42 STEINS;GATE achievements. It takes around 40-50 hours to unlock all of the achievements on Windows.
Unlocked all Achievements.
Unlocked all CGs.
Completed all endings.
Reached Mayuri's ending.
Reached Kurisu's ending.
Reached Luka's ending.
Reached Steins Gate.
Chapter 9 Clear
Unlocked 75% of CGs.
Chapter 8 Clear
Chapter 7 Clear
Reached Faris's ending.
[Phone Trigger] Received all Gero Froggy wallpapers.
[Phone Trigger] Cleared someone's mail without reading it.
Reached Suzuha's ending.
[Phone Trigger] Offered tea by Faris.
Made friends with Kurisu via email.
Chapter 6 Clear
Unlocked 50% of CGs.
Chapter 5 Clear
[Phone Trigger] Received 4 songs from a chaotic head.
[Phone Trigger] Learned why Mayuri started making costumes.
[Phone Trigger] Received 3 wallpapers of characters from a chaotic head.
Chapter 4 Clear
[Phone Trigger] Received all 13 RaiNet episode summaries.
[Phone Trigger] Asked by Kurisu to buy cup noodles twice in a row.
[Phone Trigger] Received an unusual proposition from Suzuha.
Unlocked 25% of CGs.
Learned about Luka's relationship to his sister.
[Phone Trigger] Ignored a phone call.
Made 10 mistakes while attempting to set the PhoneWave (name subject to change)'s timer.
Chapter 3 Clear
Chapter 2 Clear
Chapter 1 Clear
[Phone Trigger] Received 2 Upa wallpapers.
[Phone Trigger] Changed phone wallpaper.
[Phone Trigger] Changed ringtone.
[Phone Trigger] Replied to an email.
[Phone Trigger] Read an email.
[Phone Trigger] Viewed email send history at least once.
Prologue Clear
Started Steins;Gate.